US3677582A

US3677582A - Scaffolding clamp

Info

Publication number: US3677582A
Application number: US61101A
Authority: US
Inventors: Kenneth E Flick
Original assignee: JEWEL Mfg CO
Current assignee: JEWEL Mfg CO
Priority date: 1970-08-05
Filing date: 1970-08-05
Publication date: 1972-07-18
Anticipated expiration: 1989-07-18

Abstract

A scaffolding clamp construction in which two elongated scaffolding members are secured together at a desired angle with respect to each other by a scaffolding clamp having a pair of grooves on opposite sides of a block means, the grooves being of a depth sufficient so that the scaffolding members are substantially disposed within the grooves, there being clamping members for retaining the scaffolding members in position in the clamp. The block means may consist of two separate blocks which can be angularly adjusted with respect to each other to adjust the angular position of the scaffolding members. In the preferred form, however, the block is a solid block and bolts extend through the block on opposite diagonal corners, the bolts acting both as means for pivotally holding the clamping bars at one end and clamping the bar at its opposite end against the scaffolding member. By reason of the fact that the assemblage of the two clamp bars and the two bolts completely surround the two scaffolding members at the area where they cross each other and that the bars and bolts are of material having a relatively high tensile strength, the material of the block means need not necessarily be of such high tensile strength.

Description

United States Patent Flick [451 July 18, 1972 [54] SCAFFOLDING CLANIP [72] Inventor: Kenneth E. Flick, New Brighton, Minn. [73] Assignee: Jewel Manufacturing Company 221 Filed: Aug. 5, 1970 I 21 Appl. No.: 61,101

52 us. Cl ..2s7/49, 287/54 B FOREIGN PATENTS OR APPLICATIONS 374,320 8/1939 Italy ..287/54 B 420,021 4/1947 Italy ....287/54 B 458,566 12/1936 Great Britain ..287/54 B Primary Examiner-Andrew V. Kundrat Attorney-Frederick E. Lange, William C. Babcock and Eugene L. Johnson 57 Answer A scaffolding clamp construction in which two elongated scaffolding members are secured together at a desired angle with respect to each other by a scaffolding clamp having a pair of grooves on opposite sides of a block means, the grooves being of a depth sufficient so that the scaffolding members are substantially disposed within the grooves, there being clamping members for retaining the scafiolding members in position in the clamp. The block means may consist of two separate blocks which can be angularly adjusted with respect to each other to adjust the angular position of the scaffolding members. In the preferred form, however, the block is a solid block and bolts extend through the block on opposite diagonal corners, the bolts acting both as means for pivotally holding the clamping bars at one end and clamping the bar at its opposite end against the scaffolding member. By reason of the fact that the assemblage of the two clamp bars and the two bolts completely surround the two scafiolding members at the area where they cross each other and that the bars and bolts are of material having a relatively high tensile strength, the material of the block means need not necessarily be of such high tensile strength.

4 Claims, 5 Drawing Figures Patnted July 18, 1972 3,677,582

In 41 XNVENTOR KE/VA/ETA/E. FL/CK ATTORNEY BACKGROUND OF THE INVENTION Numerous arrangements have been proposed for clamping various scaffolding members together. In order to insure the safety of the workers on the scaffolding, it is, of course, imperative that the scaffolding members be securely held together by the clamping means. At the same time, in order to facilitate the construction of the scafiolding as quickly as possible, it is desirable that the scaffolding members can be rather quickly assembled with respect to each other in the clamp and be retained in position prior to being clamped. In many of the prior art clamps, it is necessary for the structural members to be held in position with respect to one clamping surface while the other clamping surface is being tightened against the scaffolding member. Also, some of the clamps rely entirely upon the structural strengthof the body of the clamping means for retaining the scaffolding members in their relative positions. Others of the prior art clamping members are relatively complicated, thus increasing the cost of the clamping means and adding to the complexity of the assemblage of the clamp with the scaffolding members.

SUMMARY OF THE INVENTION The present invention is concerned with a clamping means for maintaining a plurality of elongated scaffolding members together at a desired angle with respect to each other and in which the clamping means is extremely simple and reliable and facilitates very ready assembly of the scaffolding members.

The improved scaffolding clamp employs a block means with a pair of grooves on opposite sides of the block'means disposed at the desired angle with respect to each other. A clamping bar is associated with each of the grooves and serves to clamp the scaffolding member in position. The grooves are preferably of a width corresponding to the maximum width of the scaffolding member and of a depth only slightly less than the depth of the scaffolding member so that the scaffolding member projects only a small amount from the groove. Thus when the two scaffolding members are disposed in the, grooves, they are already substantially retained in place by the block means. Since much of the retention of the scaffolding members in position is accomplished by the construction of the block means, the clamping members for holding the scaffolding members in the block means may take the form of a pair of simple clamping bars, each of which is pivotally secured at one to the block means and which is clamped at its opposite end against the scaffolding member by any suitable clamping means such as a bolt and nut arrangement.

The block means can be in the form of two sections which can be adjustably secured together at any desired angle to permit angular adjustment of the scaffolding members. In the preferred embodiment, however, the block means is a solid block and the bolts extend through the block at diagonally pposite corners. The bolts act both to pivotally secure the clamping bars in position and to clamp them against the scaffolding members. Preferably, the bolts are oppositely disposed so that the head of one bolt and the nut of the opposite bolt are on the same side, the head acting as part of the means for pivotally securing the clamping bar in position and the nut acting to clamp the bar against the scaffolding member.

Where scaffolding members of circular cross-section are employed, the grooves in the block each have a semi-cylindrical lower portion conforming in radius to the radius of the scaffolding members, the grooves having a depth slightly less than twice the radius of the scaffolding members.

The clamping bars and bolts and nuts may be formed of material having substantially higher tensile strength than the material of the block means so that the scaffolding members are completely surrounded by materials having higher tensile strength.

Other objectives of the invention will become apparent from a consideration of the accompanying specification claims and drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a prospective view of the improved clamping means of the present invention;

FIG. 2 is an elevational view of the improved joint construction showing two scafiolding members in position in the clamping means and held in position in the desired relative position thereby;

FIG. 3 is a top plan view of the joint construction shown in FIG. 2;

FIG. 4 is an elevational view, partly in section, showing a modified form in which the block of the clamping means has two sections which can be angularly adjusted with respect to each other; and

FIG. 5 is a prospective view of the modification in which material has been removed from the block to decrease the weight thereof.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1 of the drawing, the clamping means is shown as comprising a block member 10 having two grooves 11 and 12 extending inwardly from the upper and lower sides thereof, respectively. The block member 10 preferably has its maximum transverse dimensions at its midpoint 13 and gradually tapers inwardly in both transverse directions as it approaches its upper and lower surfaces. This facilitates casting the unit and also provides the largest amount of material, measured in a transverse direction, at the region where the two grooves 11 and 12 would intersect each other if they overlapped in a vertical direction. A pair of

clamping bars

14 and 15 are provided for clamping the scaffolding members in position. These

clamping bars

14 and 15 extend diagonally across the

grooves

11 and 15, respectively, and are pivotally secured to the block members so that they can be swung to one side to permit the insertion of the scaffolding members. The

clamping bars

14 and 15 are pivotally secured to the block and are clamped across the scaffolding members by a pair of

bolts

19 and 20. The bolt 19 is provided with a head 21 and a nut 22 threadedly secured to the bolt. Similarly, the bolt 20 is provided with a head 24 and a nut 25 thr'eadedly secured to the bolt. Itwill be noted that the

bolts

19 and 20 extend entirely through the block 10 on opposite diagonal comers thereof. It will also be noted that the

bolts

19 and 20 are oppositely disposed so that the head 21 of bolt 19 is on the upper side of the block 10, while the head 24 of bolt 20 is on the lower side of block 10. It is also to be noted that the

heads

21 and 24 of

bolts

19 and 20 are spaced from the adjacent surfaces of the block 10 by an amount somewhat in excess of the thickness of the

clamping bars

14 and 15. The clamping bar 14 has an aperture therethrough at one end, which aperture surrounds the bolt between the head 21 and the adjacent block surface. Similarly the clamping bar 15 has an aperture surrounding the bolt 20 and is disposed between the head 24 and the adjacent block surface. The

bolts

19 and 20 serve to pivotally retain the

clamping bars

14 and 15 in position. The unit is assembled by placing each clamping bar inposition with its aperture aligned with the aperture through the block 1.0 in which the bolt is disposed, and driving the bolt through the block. The bolt may be provided with any suitable means for retaining it in position in the block. For example, the bolt may have a plurality of Iongitudinal ribs disposed about its periphery at an intermediate position thereof, which ribs penetrate the material of the block and prevent longitudinal or rotational movement of the bolt with respect to the block.

Referring to FIGS. 1 and 2, it will be noted that the clamping bar 14 is curved upwardly adjacent to its midpoint as it extends away from the area at which it is pivotally connected to the block. This curvature tends to conform with the curvature of the scaffolding member. The remaining portion of the clamp 14 is relatively flat. At its opposite end, it is provided with a slot 30 which extends inwardly from one side of the clamping bar and is of a width appreciably greater than the diameter of the bolt 20. The slot 30 extends generally transversely of the clamping bar 14 and is so disposed with respect to the bolt 20 that the slot 30 will pass around the bolt 20. When this is done, the clamping member 14 is in a position where it can be engaged by the nut 25. The clamping bar 15 is of similar construction and is provided with a slot 31 which extends around the bolt 19 and permits the clamping bar 15 to be clamped by the nut 22.

The clamp of FIG. 1 is designed to be used with scaffolding members of circular cross-section. The interior portions of each of the grooves 11 and 12 is accordingly of semi-circular cross-section and of a radius substantially corresponding to the radius of the scaffolding member with which it is to be used. Furthermore, the depth of each groove 11 and 12 is slightly less than twice the radius of the scaffolding member so that when a scaffolding member is disposed therein, it will project only a short distance out of the groove.

FIGS. 2 and 3 show a joint construction employing the improved clamp with two

scaffolding members

35 and 36 retained in position thereby. It will be noted that each of these

scaffolding members

35 and 36 is a tubular cross-section and that the radius of the tubular scaffolding member is substantially the same as the radius of the semi-circular portion of the grooves 11 and 12 in which the

scaffolding members

35 and 36 are disposed. It will also be noted that the

bars

14 and 15 have been clamped against the

scaffolding members

35 and 36 by

nuts

25 and 22 respectively.

In using the clamping devices, it will be assumed that the scaffolding pipe 36 is already in position and it is desired to clamp at right angles thereto the scaffolding pipe 35. The block is positioned on the pipe 36 with the pipe 36 disposed within the groove 12. The pipe 35 is now placed within the groove 11. Inasmuch as the radius of pipe 35 substantially corresponds to the maximum width of the slot 11 and the same applies to the slot 12 and pipe 36, and since the grooves 11 and 12 are sufficiently deep that the

pipes

35 and 36 project only a slight distance therefrom, it will be readily apparent that before the clamping bars 14 and 15 are applied, the

pipes

35 and 36 are held firmly with respect to each other. It is, of course, understood that at some spaced point, at the end of the scaffolding section formed by pipe 35 or of which pipe 35 is a part, there is another similar joint being made by another workman. Consequently, the pipe 35 will be supported in at least two points and this support with respect to pipe 36 and any other pipes parallel thereto will be rather firm. The importance of this is that the workman does not have to hold either

pipes

35 or 36 or block 10 while heis fastening straps 14 and 15. Due to the clamping bar 14 being freely pivotable about the bolt 19, beneath the bolt head 21, it is possible to swing the clamp 14 into the position shown in FIGS. 2 and 3, in which position the slot 30 embraces the threaded end of bolt beneath the nut 25. The nut is now tightened down and due to the flexing of the bar 14, the outer portion of the bar bends down from the horizontal position in which it is shown in FIG. 1, as shown in FIG. 2. The result is that the scaffolding pipe 35 is held firmly in position within the groove 11.

Similarly, the clamping bar 15 is swung about its pivotal connection with bolt 20 so that the slot 31 thereof straddles the bolt 19 and the nut 22 is then tightened to free the clamping bar 15 and cause it to freely engage pipe 36.

One important feature of my invention is that the clamping bars 14 and 15 and the

bolts

19 and 20, including the nuts 22 and 25, are fonned of steel having a relatively high tensile strength. The block itself may be formed of material having a lower tensile strength. In one example, an aluminum magnesium alloy, commercially referred to as Al-Mag 35 was employed to form the block 10. This material, while having adequate strength to fully support

pipes

36 and 35 with respect to each other, does not have as great a tensile strength as measured in pounds per square inch as

bars

14 and 15 and the

bolts

19 and 20. It will furthermore be noted that because of the diagonal'disposition of the clamping bars 14 and 15, the

scaffolding pipes

35 and 36 are encircled between clamping

bars

14 and 15 and the

bolts

19 and 20.

MODIFICATION OF FIGURE 4 In the modification of FIG. 4, provision is made for adjusting the angular position at which the scafi'olding members, such as

pipes

35 and 36, are held. In this case, the block means comprises two

separate blocks

40 and 41, which collectively have the same general shape as block 10 of the preferred embodiment of FIGS. 1, 2 and 3. Block 40 has a groove 42 therein and block 41 has a similar groove 43 therein. The two blocks are generally of the same collective configuration as block 10 and the grooves are of the same size with respect to the scaffolding members as grooves 11 and 12 in the embodiment previously described. The, two

blocks

40 and 41 have cooperating interfaces which abut each other along a plane 44. The two

blocks

40 and 41 are held together by a screw which is rotatably mounted in block 40 and is threadedly engaged with block 41. It will be readily apparent that when screw 46 is tightened, blocks 40 and 41 are held firmly with respect to each other. Upon loosening screw 36, however, it is possible to rotate the

blocks

40 and 41 with respect to each other about an axis defined by the central longitudinal axis of screw 46. It is to be understood that the screw 46 is located centrally of the two

blocks

40 and 41. While the

blocks

40 and 41 have been shown, for convenience in illustration, as being in a position in which the

grooves

42 and 43 are parallel to each other, it is to be understood that normally they will be disposed at an angular relationship to each there corresponding to the desired angular relationship between the scaffolding members secured therein.

As with the previously described embodiment, there are two clamping

bars

54 and 55. These bars, like

bars

14 and 15, are pivotally connected to the block means at one end and are clamped against the pipe at the other end. Since, however, there are two

separate blocks

40 and 41 which are angularly adjusted with respect to each other, it is not possible to have a single pair of bolts extending completely through the block. Thus, four bolts are used. The bolts associated with the block 40 are designated by the

reference numerals

56 and 57 and those associated with block 40 by the reference numerals 58 and S9. The

bolts

56, 57, 58 and 59 each have heads and are secured in the blocks, as shown in connection with bolt 58, by casting the bolts in position when the

blocks

40 and 41 are cast. It will be noted that bolt 58 has a head 60 and is cast into the material so as to prevent the bolt 58 from being withdrawn.

Unlike the arrangement of FIGS. 1 to 3 in which the heads of bolts are used in connection with pivotal mounting of the clamping bars to the clamp body structure, the

bolts

56, 57, 58 and 59 all have separate nuts, these being indicated by the

reference numerals

62, 63, 64 and 65, respectively. Since the clamping bars 54 and 55 have

slots

67 and 68 corresponding to the

slots

30 and 31, it is not necessary for all of the nuts 62 to 65 to be removed. The nuts 63 and 64 remain in position on their respective bolts spaced sufiiciently from the associated

block members

40 and 41, respectively, to permit free pivotal movement of the clamping bars 54 and 55.

In use, the screw 46 is loosened and the

blocks

40 and 41 are angularly adjusted with respect to each other so that the

grooves

42 and 43 assume the specific angular relationship desired between the scaffolding members to be secured by the clamp. The screw is then tightened to retain

members

40 and 41 in this desired angular relationship. The procedure from this point on is very much the same as in connection with the clamp of FIGS. 1 through 3. The block assembly is placed on the scaffolding pipe in position, the groove 43 of block 41 embracing such pipe. The next pipe is then placed in position in groove 42 of block 40. The

straps

54 and 55 are then clamped against the pipe in

grooves

42 and 43 by tightening

nuts

62 and 65.

While the arrangement of FIG. 4 is not as rugged structurally due to the fact that the bolts do not extend entirely through the block as with the arrangement of FIGS. 1 to 3, it

MODIFICATION OF FIGURE 5 The unit of FIG. 5 is similar to that of FIG. 1 except that portions have been cut away to lighten the clamp without materially reducing the strength thereof. The block in this figure is designated by the reference numeral 70. This block corresponds to block of the preferred species of FIGS. 1 to 3. The clamping bars, being identical to those in the preferred species have been designated by the same numerals, 14 and 15. The manner in which the clamping bars 14 and 15 are secured to block 70 and the manner in which they are utilized in clamping scaffolding members in position is the same as in the species of FIGS. l to 3 and will not be again described. The only difference between block 70 and block 10 of the species of FIGS. l to 3 is that the portion of any wall parallel to and adjacent to one of the grooves has intermediate portion and an end wall portion 76. Due to the end wall portion 76, the bolt retaining portion 75 and the reinforcing rib 73, the wall 74 adjacent the groove ll is adequately supported. As pointed out in connection with the description of FIGS. 1 to 3, the

bolts

19 and 20 and the clamping bars 14 and 15 provide an encircling band of steel around the cross-scaffolding members so that the primary function of the block is to position the members in their position and to serve as an anchor for the bolts and clamping bars. Thus, it is not necessary to employ as much material in the body member 70 as would be the case if this body member was being relied upon to provide the primary means for clamping the scaffolding members in position. Thus, while the unit of FIG. 5 is substantially lighter than the unit of FIG. 1, it has adequate structural strength for retaining scaffolding members in position and has all of the other advantages described in connection with the embodiment of FIGS. l to 3.

CONCLUSION It will be seen that the scaffolding clamp of the present invention provides for very easy assembly of two scaffolding members due to the fact that the scaffolding members are substantially retained in position once they are placed in position with respect to the clamp. Furthermore, the unit is extremely strong in that the members are held in position not only by the material of the main block of the clamp, but are also encircled by members of high tensile strength Furthermore, the construction even where adjustability of the angular position of the scaffolding members is provided for, is extremely simple.

While I have shown certain embodiments for the purpose of illustration, it is to be understood that the invention is limited solely by the scope of the amended claims.

I claim as my invention:

l. A scaffolding clamp for securing two elongated scaffolding members together at a desired angle with respect to each other, said clamp comprising:

a solid substantially polygonal block having a pair of grooves in diametrically opposite sides thereof and disposed at said desired angle with respect to each other, each of said grooves being of a width substantially corresponding to the maximum transverse dimension of the scaffolding member disposed therein and having a symmetrical cross-sectional configuration on each side of the longitudinal axis of the groove for the length of the groove and a uniform depth along the length thereof and only slightly less than the thickness of the scaffolding member therein so that each scaffolding member projects only a relatively small distance out of said block means,

a pair of clamping bars extending generally parallel to each other on opposite sides of said block, each extending diagonally across one of said grooves, said bars being of material having a relatively high tensile strength as compared with the material of which said block is formed, and pair of bolts extending through cylindrical apertures in said solid block at diagonally opposite corners thereof with the terminal portions of said bolts projecting beyond said block, said cylindrical apertures extending uninterruptedly thru the body of said solid block and terminating at said opposite corners, each bolt having a head at one terminal portion and a nut threadedly secured to the bolt at its opposite terminal portion, the heads and nuts of said bolts being disposed on opposite sides of said block and being relatively reversed with respect to each other so that the head of one bolt and the nut of the other are on the same side, each of said clamping bars having an aperture therethrough at one end and being pivotally disposed over an associated bolt between the head thereof and the adjacent block surface, the head being spaced from the block sufiiciently to permit free swinging of the clamping bar pivotally secured thereto, said bolts and the nuts secured thereto likewise being of material of relatively high tensile strength so that when scaffolding members are placed in said grooves and secured in place by said clamping bars and said bolts and nuts, the crossed scaffolding members are surrounded. by a clamping assembly composed of said clamping bars and said bolts and nuts, which clamping assembly has a relatively high tensile strength as compared with that of the block.

2. The scaffolding 'clamp of claim l. in which each clamping bar is provided with a slot extending in from one side thereof adjacent the end of the bar opposite to the end at which the bar is pivoted, said slot being of such configuration and so disposed as to enable it to pass over the bolt opposite to that to which it is pivoted so that the nut thereof can engage said bar.

' 3. The scafiolding clamp of claim 1 in which spaced portions of the block adjacent each wall of the grooves are cut away to reduce the weight of the block without substantially decreasing the strength thereof.

4. A scaffolding clamp for securing; two elongated scaffolding members together at a desired angle with respect to each other, said clamp comprising:

a block having a pair of grooves in opposite sides thereof and disposed at said desired angle with respect to each other, said block having spaced portions thereof adjacent each wall of the grooves cut away to reduce the weight of the block without substantially decreasing the strength thereof, said cut-away spaced portions adjacent each wall being spaced from each other by a diagonal rib,

a pair of clamping bars on opposite sides of said block, each extending diagonally across one of said grooves, said bars being of material having a relatively high tensile strength as compared with the material of which said block is formed, and

a pair of bolts extending through said block at diagonally opposite corners thereof, each bolt having a head and a nut threadedly secured to the bolt, the heads and nuts of said bolts being disposed on opposite sides of said block and being relatively reversed with respect to each other so that the head of one bolt and the nut of the other are on the same side, each of said clamping bars having an aperture therethrough at one end and being pivotally disposed over an associated bolt between the head thereof and the adjacent block surface, the head being spaced from the block sufficiently to permit free swinging of the clamping bar pivotally secured thereto.

Claims

1. A scaffolding clamp for securing two elongated scaffolding members together at a desired angle with respect to each other, said clamp comprising: a solid substantially polygonal block having a pair of grooves in diametrically opposite sides thereof and disposed at said desired angle with respect to each other, each of said grooves being of a width substantially corresponding to the maximum transverse dimension of the scaffolding member disposed therein and having a symmetrical cross-sectional configuration on each side of the longitudinal axis of the groove for the length of the groove and a uniform depth along the length thereof and only slightly less than the thickness of the scaffolding member therein so that each scaffolding member projects only a relatively small distance out of said block means, a pair of clamping bars extending generally parallel to each other on opposite sides of said block, each extending diagonally across one of said grooves, said bars being of material having a relatively high tensile strength as compared with the material of which said block is formed, and a pair of bolts extending through cylindrical apertures in said solid block at diagonally opposite corners thereof with the terminal portions of said bolts projecting beyond said block, said cylindrical apertures extending uninterruptedly thru the body of said solid block and terminating at said opposite corners, each bolt having a head at one terminal portion and a nut threadedly secured to the bolt at its opposite terminal portion, the heads and nuts of said bolts being disposed on opposite sides of said block and being relatively reversed with respect to each other so that the head of one bolt and the nut of the other are on the same side, each of said clamping bars having an aperture therethrough at one end and being pivotally disposed over an associated bolt between the head thereof and the adjacent block surface, the head being spaced from the block sufficiently to permit free swinging of the clamping bar pivotally secured thereto, said bolts and the nuts secured thereto likewise being of material of relatively high tensile strength so that when scaffolding members are placed in said grooves and secured in place by said clamping bars and said bolts and nuts, the crossed scaffolding members are surrounded by a clamping assembly composed of said clamping bars and said bolts and nuts, which clamping assembly has a relatively high tensile strength as compared with that of the block.

2. The scaffolding clamp of claim 1 in which each clamping bar is provided with a slot extending in from one side thereof adjacent the end of the bar opposite to the end at which the bar is pivoted, said slot being of such configuration and so disposeD as to enable it to pass over the bolt opposite to that to which it is pivoted so that the nut thereof can engage said bar.

3. The scaffolding clamp of claim 1 in which spaced portions of the block adjacent each wall of the grooves are cut away to reduce the weight of the block without substantially decreasing the strength thereof.

4. A scaffolding clamp for securing two elongated scaffolding members together at a desired angle with respect to each other, said clamp comprising: a block having a pair of grooves in opposite sides thereof and disposed at said desired angle with respect to each other, said block having spaced portions thereof adjacent each wall of the grooves cut away to reduce the weight of the block without substantially decreasing the strength thereof, said cut-away spaced portions adjacent each wall being spaced from each other by a diagonal rib, a pair of clamping bars on opposite sides of said block, each extending diagonally across one of said grooves, said bars being of material having a relatively high tensile strength as compared with the material of which said block is formed, and a pair of bolts extending through said block at diagonally opposite corners thereof, each bolt having a head and a nut threadedly secured to the bolt, the heads and nuts of said bolts being disposed on opposite sides of said block and being relatively reversed with respect to each other so that the head of one bolt and the nut of the other are on the same side, each of said clamping bars having an aperture therethrough at one end and being pivotally disposed over an associated bolt between the head thereof and the adjacent block surface, the head being spaced from the block sufficiently to permit free swinging of the clamping bar pivotally secured thereto.