US3751834A

US3751834A - Spread-legged staple retainer for excavating tooth

Info

Publication number: US3751834A
Application number: US00215739A
Authority: US
Inventors: G Petersen
Original assignee: Individual
Current assignee: Individual
Priority date: 1972-01-06
Filing date: 1972-01-06
Publication date: 1973-08-14
Anticipated expiration: 1990-08-14
Also published as: DE2261910A1; SU426378A3; AU5016672A; GB1416721A; FR2167784A1; IT976743B; AU450843B2

Abstract

A retainer of approximately U-shape but with the legs initially slightly diverging or converging, detachably secures the proximal part of an excavating tooth within a complementary recess in its holder. The holder has holes through which the legs of the retainer fit in approximately parallel relation to each other, thereby stressing the legs from their diverging or converging position and causing them frictionally to engage the walls of the holes so that the retainer does not move inward or outward unintentionally. One or both legs of the retainer or portions thereof engage in notches formed in the proximal part of the tooth only when the retainer is in its inward position. The legs are offset so that when the retainer is depressed an upper offset portion engages in the notches in the tooth and prevents the withdrawal of the tooth. When the retainer is partially withdrawn from the holder, the lower offset portions of the retainer legs do not fit in the notches in the tooth, and hence the tooth may be withdrawn. Means is provided to prevent complete unintentional withdrawal of the retainer from the holder.

Description

llmted States Patent 11 1 1 1 3,751,834 Petersen Aug. 14, 1973 [54] SPREAD-LEGGED STAPLE RETAINER FOR 3,550,293 12/1970 Helton 37/142 R X EXCAVATING TOOTH Primary Examiner-Edgar S. Burr [76 Inventor: Gerald A. Petersen Villa Pen 0 1a,

1 Chem des saucy venceg p Attorney-Gregg, Hendncson & Caplan France 57 ABSTRACT [22] Filed: Jan. 6, 1972 1 A retainer of approx1mately U-shape but with the legs 1 pp 215,739 initially slightly diverging or converging, detachably secures the proximal part of an excavating tooth within 52 us. (:1. 37/142 R, 85/83 a mess in its The has 51 1m. (:1 E02f 9/28 hwugh which the legs the retainer fit [58] Field of Search 37/142; 85/83; pmxiinatdy Pmel i f F her, i' 24/73 SM stressmg the legs from their diverging or converging po sition and causing them frictionally to engage the walls of the holes so that the retainer does not move inward [56] References Cited m d t a on r both] h or 0 war unm en I011 y. e o egs o e re- UNITED STATES PATENTS tainer or portions thereof engage in notches formed in 1,685,126 9/1928 Evans 85/83 the proximal part of the tooth only when the retainer a if g2 is in its inward position. The legs are offset so that when 5248 1/1962 S fs et 37/142 A x the retainer is depressed an upper offset portion en- 3 021 627 2/1962 1211115: I 85 83 gases in the aches in and prevents the with 3:091:044 5/1963 Penote ct 31m 37/142 R drawal of the tooth. When the retainer is partially with- 3,281,972 11/1966 Kerestes 37/141 R drawn from t holder. the lower Offset Portions of the 3,325,926 6/1967 Wilson 37/142 R retainer legs do not fit in the notches in the tooth, and 3,397,012 8/1968 Krekeler 37/142 R X hence the tooth may be withdrawn. Means is provided 3,400,476 /19 eterse 142 R to prevent complete unintentional withdrawal of the 1 7 retainer from the holder. ar en 3,497,973 3/1970 Campbell.... 37/141 R 8 Claims, 17 Drawing Figures 5/ 69 58 59 22 36 K 1\ l i Q f If 59 54 A 2 7/ 34 2 46 I r I I l i 77 -1 55 K PATENIED M1 41% 3'. 751 .834

SHEET 3 0f 3 SPREAD-LEGGED STAPLE RETAINER FOR EXCAVATING TOOTH This invention relates to a new and improved spreadlegged staple retainer for excavating tooth. More particularly, the invention relates to a staple-shaped retainer, the legs of which initially either diverge or converge and which is inserted in parallel holes in a tooth holder. The tooth holder has one or more recesses which receive the shank or proximal part of the tooth in such manner that one or both legs of the retainer fit into notches in the tooth when the retainer is fully inserted in the holder. On the other hand, when the retainer is partially withdrawn the legs thereof do not fit into the notches, and hence the tooth is not held in the holder.

It is thus a principal feature of the present invention that the retainer is formed with offset legs so that the upper end of each leg comprises a retainer portion which, when the retainer is fully inserted in the holder, is operative and the lower portions of the legs are offset relative to the upper portion so that when the retainer is partially withdrawn the lower portions of the legs do not fit into the notches and the retainer is inoperative.

Another feature of the invention is the fact that the legs are fabricated so that they initially either diverge or converge and the holes in the retainer are approximately parallel, thereby requiring that the. legs be distorted from their initial position, and this distortion causes a frictional engagement of the legs with the walls of the holes in which the legs are inserted and hence frictionally prevents unintentional movement of the retainer from operative to inoperative position.

Another feature of the invention is the fact that the top of the retainer is preferably formed in such manner as to enhance the tendency of the legs to fit into the notches in the operative position of the retainer.

Still another feature of the invention is the fact that one leg of the retainer is preferably made longer than the other, and by inserting the longer leg in one hole and then moving the shorter leg either toward or away from the longer leg the shorter leg conveniently be installed in its hole without the use of special effort or special tools.

Still another feature of the invention is the provision of a protuberance on the wall of the hole in the holder in which the retainer is inserted and which is engaged by the retainer and indicates to the user that the retainer is withdrawn to inoperative position.

still another feature of the invention is the shape of the holes of the retainer so that dirt does not tend to lodge therein to interfere with the retainer moving between operative and inoperative positions. Thus the cavities are outwardly diverging so that the dirt tends to fall out of the retainer without packing inside.

Earth handling equipment of which typical-examples are buckets, angers, trenchers, dredging and mining machinery, and the like, have separate teeth and tooth holders. The holder is fixed to a portion of the earth excavating equipment such as a lip or a plate as by means of bolts or welding. The teeth absorb most of the wear of the digging action and are removable from the holder from time to time for sharpening or replacement. Accordingly, means is provided for a semipermanent attachment of the holder to the lip of the bucket or auger and a readily releasible means of attachment to hold the tooth in the tooth holder. The

present invention provides both such means where required.

It is a principal feature of the invention to provide a staple-like retainer to hold the tooth in a recess in the holder, the legs of the retainer fitting into holes of the holder and into notches in the margins of the proximal portion of the tooth. Thus the tooth is restrained from removal so long as the retainer is in its operative position. At the same time, the retainer may readily be partially withdrawn when it is necessary to remove the tooth.

A principal advantage of the retaining means for the tooth is, therefore, the fact that it is rapidly installed and removed and when in place securely holds the tooth in position against unintentional dislodgement.

Still another advantage of the retainer is the fact that it is inexpensive and can readily be replaced if the original retainer is lost or damaged.

Another advantage of the invention is the fact that no special tools are required to install either the holder on the lip of the earth moving equipment or to install the retainer in the holder.

It is, further, a principal purpose of the present invention to provide means of attachment of a tooth holder to a permanent portion of excavating equipment by means of a plow bolt which fits into one surface of the holder and extends through holes in the lip of the equipment and then through the opposite portion of the holder. A recess is formed in the exposed surface of the opposite portion to receive a nut which fits on the bolt. Spoil exit areas communicate between said recess and the exterior of the holder so that dirt does not harden in the recess and inhibit necessary removal of the nut. The foregoing is a preferred means for attachment of the holder to an auger intended to dig in clay. However, the holder may be bolted or welded to or formed integral with the bucket, auger or other device.

It is, accordingly, a principal purpose of the invention to provide means for fastening the holder to a permanent portion of earth excavating equipment such as the lip of a bucket in such manner as to make the attachment secure but to still permit the holder to be removed on those infrequent occasions when it is necessary to replace the same.

Other objects of the present invention will become apparent upon reading the following specification and referring to the accompanying drawings in which similar characters of reference represent corresponding parts in each of the several views.

In the drawings:

FIG. 1 is a top plan view of one form of the invention partially broken away to reveal internal construction.

FIG. 2 is a sectional view taken substantially along the line 2-2 in FIG. 1.

FIG. 3 is a transverse sectional view taken substan tially along the line 3-3 of FIG. 2 showing the retainer in operative position.

FIG. 4 is a view similar to FIG. 3 showing the retainer in inoperative position.

FIG. 5 is a perspective view of a retainer used in the modification of FIG. I showing the same from the holder and with the legs converging.

FIGS. 6-9 are views similar to FIG. 11-4 of a modification.

FIG. 10 is a view similar to FIG. 5 showing the legs of the retainer of FIG. 6 diverging prior to insertion in the holder.

FIGS. 11-17 are, respectively, perspective views of modifications of the retainer as hereinafter described in detail.

Directing attention first to the modification shown in FIG. 1, the assembly consists of three members, a replaceable digging tooth 21, a holder 22 which receives the tooth and a retainer 23 which detachably secures the tooth in place in the holder.

In the form of invention shown in FIGS. 1-3, holder 22 is bolted to an auger, bucket or the like and has a bottom portion 27 and a top portion 28 separated therefrom by a slot 29 which extends from the rear of the holder forwardly thereof with a connecting portion 31 joining the top and bottom. The lip on a bucket, auger or other equipment fills the slot. Aligned holes 32 are formed in top and bottom portions 27, 26 as well as in the lip (not shown) to receive bolts (not shown). In a preferred form, the holes 32 on the bottom surface are formed with countersinks 33 and with square holes above the countersinks to receive plow bolts (not shown) which have complementary heads and shanks, but the shape of the holes and the optional use of plow bolts are subject to modification. The top surface of top portion 28 is formed with recesses 34 each shaped to receive nuts which hold the bolts in place with sufficient clearance so that a conventional socket type wrench may be inserted in the recess 34 to turn the nut. If the holder 22 becomes worn, it may be removed by removing the bolts, but this is done very infrequently. I-Iolder 22 may be welded to or formed integrally with the lip of the equipment.

Recess 39 is formed extending rearwardly from the forward end of the distal portion of holder 22, the shape of recess 39 accommodating the proximal end of the particular tooth 21 with which the holder is employed. In the form shown in FIG. 1, the distal portion of holder 22 has a top portion 41 and a bottom portion 42 which are spaced from each other and connected by a central web 43. The holder viewed in end elevation resembles the letter H turned 90.

To accommodate retainer 23, holes 46 are formed in the top portion 42 spaced apart the width of the top of the retainer and communicate with recess 39. These holes are slightly wider than the thickness of the retainer legs. Protector 44 is formed extending transversely of the top of top portion 41 immediately forwardly of retainer 23 to absorb abrasion of the soil which might otherwise dislodge or damage the retainer. As shown in FIG. 2, protector 44 slants upwardrearward in a ramp which rises above the elevation of retainer 23, then is stepped downwardly to the rear of its highest elevation to a level about the same as the retainer. The bottom portion 41 is also formed with holes 48.

Directing attention particularly to FIG. 3, it will be seen that the inner wall of each hole 46 is approximately straight, whereas the outer walls of the web 43 converge inwardly. Hence for practical purposes holes 46 are outwardly diverging and any dirt which tends to be trapped therein is readily removed. For purposes which are hereinafter made clear, protuberances 47 are formed on the outwardly facing walls of web 43 adjacent the upper end thereof.

With further reference to FIG. 3, it will be seen that the walls of holes 48 are downwardly diverging so that any dirt which tends to be trapped therein is readily pushed out when the retainer is moved. Further, if portions of the retainer should break, they readily drop through the

holes

46 or 48.

The form of tooth 21 of FIG. 1 which fits holder 22 has forwardly converging top and bottom

distal surfaces

51 and 52 when viewed in top plan with a blunt transverse forward cutting edge 55. In the form shown in FIG. 1-3, the side edges are generally parallel with lateral extensions 53 formed on either side at the distal end of the tooth. It will be understood, that ifa plurality of teeth 21 are positioned side by side, the lateral extensions 53 may be located abutting to present an almost continuous blade made up of a plurality of cutting edges 55. Nevertheless, each tooth holder 22 is narrower than the total width of the edge 55 and hence may be so located with a separation between the adjacent holders. In a preferred form of tooth, a central spine 54 on surface 51 originates adjacent the cutting edge 55 and gradually rises in elevation. Further, immediately forward of the holder 26 there is a transverse thickening 69 which merges with spine 54in large radii.

In the fonn of the invention best shown in FIG. 2, the distal portion of the tooth 21 is at an oblique angle with respect to the proximal portion and the bottom surface 42 of the distal portion of the tooth is approximately coplanar with the bottom of the bottom portion 26 of the holder. The recess 39, however, slants upwardly relative to the bottom surface of bottom portion 27. It will be understood that this feature of the construction is optional.

The top and

bottom surfaces

56, 57 of the proximal end of tooth 21 are preferably parallel and fit within the recess 39 between upper and

lower portions

41, 42. The side edges are continuations of the side edges of the distal end. A rectangular slot 58 is formed extending forwardly from the rearward end of the tooth 21, dividing the proximal end of the tooth into two prongs 59 which are substantially rectangular in transverse cross-section. The back ends 61 of the prongs 59 fit against the back of the recess 39 and are shaped complementary thereto. As an important feature of the invention, notches 62 are formed in the inward facing side edges of slot 58 in alignment with holes 46. Notches 62 are of a depth about equal to the thickness of retainer 23. Shoulders 63 behind notches 62 prevent the tooth from being removed from the holder when the retainer is in place.

Retainer 23 is preferably formed of flat, wire-stock steel which is quite resilient. In its initial or relaxed position, shown in FIG. 5, the legs converge inwardly at an angle of about 10 with respect to the vertical. The bottom portion 72 of each leg is displaced inwardly relative to the upper portion 71 by the depth of notch 62 and there is a short connecting outwardly upwardly slanted portion 73 there-between. The top of each leg is connected to the top of the opposite leg by a top portion which, in the form of the invention shown in FIG. 5, resembles a letter S in plan. This shape gives further resiliency and springiness to the legs of the retainer.

Directing attention to the retainer shown in FIG. 5, at the upper end of the upper portion 71 there is an outward bend 74. In top plan, proceeding outwardly from each bend 74 is a semi-circular curve 76. The semi-circular curves on the two legs are disposed in opposite directions. Connecting the semi-circular curves 76 is a diagonal connection 77.

In a preferred form of the invention, one bottom portion 72 is longer than the other. Thus in FIG. 5 it will be observed that the left leg 72 is somewhat longer than the right leg by an extension 78. Directing attention now to the assembled position of the retainer, the longer leg extension 78 is first partially inserted in left hole 46 and the shorter leg is then pushed away from the longer leg so that it slips into the right hole 46. The retainer 23 is then pushed downwardly until the offsets 73 snap under the protuberances 47. The retainer is now in the position shown in FIG. 4 where it is inoperative insofar as holding the tooth in place. The lower portions 72 of the legs, being offset inwardly relative to the upper portions, are close against the web 43 and the offsets 73 are up against the protuberances 47. Hence the protuberances 47 limit unintentional removal of the retainer 23. When the user feels the offsets 73 engage the protuberances 47, he knows that the retainer 23 is in retracted or inoperative position and does not need to retract it further. When the retainer is pushed into full inward or operative position shown in FIG. 3, the upper portions 71 of the legs fit into the notches 62 in. the prongs. So long as the retainer is in the position of FIG. 3, the tooth cannot be removed because the upper portions 71 of the legs fitting against shoulders 63 prevent such movement. On the other hand, when it is necessary to remove the tooth, the retainer 23 is pulled up ward to the position of FIG. 4. It will be seen with reference to FIG. 3 that the top elevation of web 43 is sufficiently low so that a prying tool such as a screw-driver blade can be inserted under the top diagonal 77 of the retainer to lift the same.

In the form of the invention shown in FIGS. 6-10, tooth 21a is similar to that shown in US. Pat. No. 3,349,508. The distal of the tooth 21a is rectangular in plan having a broad cutting edge with parallel side edges and lateral extensions 53a at the far distal end and the bottom 52a is generally flat. The top 51a is formed with a central longitudinal spine 86 which merges in a transverse protuberance 87 extending out to the side edges. The proximal end of the tooth is inverted T shaped in cross-section and slants upwardly relative to the distal at about a 22 angle. The proximal has an upstanding leg 88 terminating in a shoulder 89 near, but spaced forward from, the rearward end and has laterally extending feet 91. The outer edges of feet 91 and also of spine 86 taper inward rearward and there are curved shoulders 92 when viewed in plan where the outer edges merge with protuberance 87. A central longitudinal groove 93 is formed in the underside of the proximal end of the tooth. As shown in FIG. 7, top surfaces 94 to either side of slot 96 are flat. An opening 97 is provided to the rear of shoulder 89 to provide access for a tool to drive the tooth out of the holder. Inward movement of the tooth is.. accurately limited by shoulders 98 complementary to shoulders 92 formed at the forward opening of recess 39a (see FIG. 6). To protect the retainer 23a, hereinafter described, from abrasion, a transverse strap 99 bridges slot 96 immediately forward of the retainer. To hold the tooth against lateral displacement ridge 100 is formed nesting in groove 93 formed on the top of the thickened lower portion 103 of holder 22a below recess 390.

To retain tooth 21a, notches 101 are formed in the inner edges of top surfaces 94 facing slot 96 and aligned with notches 102 in the outer edges of feet 91. Downward opening holes 104 are formed in lower portion 103 of holder 22a below recess 39a to receive the lower ends of the legs of the retainer as hereinafter described. Protuberances 106 (similar in shape and function to 47 of th preceding modification) are formed in the outer walls of notches 101.

Retainer 23a is similar to retainer 23 with two exceptions. The legs diverge outwardly instead of inwardly at about 10 angles. The upper portion 71a of each leg is offset inward relative to lower portion 72a. Hence holes 104 are offset outward relative to notches 101 and protuberances 106 are on the outside walls of notches 101 to be engeged by slanted connecting portions 73.

The

inserts

23, 23a are subject to considerable variation as is shown in FIGS. 11-17. The forms shown in FIGS. 11-15 and 17 are for use with the tooth and holder of FIGS. 6-9, but it is apparent that with suitable modification the forms of retainer may be changed to retain a tooth of the shape of FIGS. 1-4 in an appropri ate holder. These changes involve slanting the legs inwardly rather than outwardly and making the lower leg portions offset inwardly relative to the upper leg portions. The form shown in FIG. 16 is described below.

Directing attention to FIG. 11, it will be seen that from the bend 74b the connecting portion 76bextends inwardly horizontally through about the middle of the retainer and then is bent in a circle 77b, one end of the circle being disposed under the other end of the circle. The curve 77b provides springiness to the retainer. In the form shown in FIG. 12, the portions above the bend 74c extend inward a short distance and a U-shaped connecting portion 770 extends in one direction or the other.

In FIG. 13, a bend 111 is formed slanted upwardly v outwardly at an angle of about 1 I0 at the upper end of upper portion 71d and extends in an upwardoutward stretch 114 to a bend 112 which is about I60 of are. The horizontal connecting portion 113 is at approximately right angles to the longitudinal axis of the retainer 23d. The distance between the bends 112 is greater than the distance between the lower ends of the lower leg portions 72d. In all of these modifications the legs diverge outwardly at an angle of about 10 with respect to the vertical so that the total included angle be tween the two legs is about 20.

In the retainer 23e shown in FIG. 14 the parts are similar to those in FIG. 13 except that the stretch 114e is more nearly parallel to and underlies the connecting portion 1131;.

The retainer 23f shown in FIG. 15 is similar to the retainer 23d of FIG. 13 except that, for use with a tooth and holder similar to that of FIGS. 6-9, at the upper end of lower leg portion 72 an approximately inwardly directed short stretch 116 is formed and this is followed proceeding upwardly by an inwardly offset stretch 117, the upper end of which is connected by a short stretch 118 similar to 116 to the upper leg portions 71f. The portions 117 fit in the notches (not shown but similar to notches 102) in the tooth.

FIG. 16 shows a retainer 23g similar to retainer 23] of FIG. 15 except that it is intended for use with double pronged teeth and corresponding holders of the type shown in FIGS. 1-4. Thus the legs of the retainer converge downwardly and the offsets 1173 are disposed outwardly rather than inwardly relative to upper leg portion 71g.

In FIG. 17, the leg construction of tooth 23h is similar to that of FIG. 10. The connecting portion 77): extends directly across between the bends 74h. The

springiness of the material of construction of the retainer, and the use of the extension 78h on one leg, makes it possible for the retainer to be stressed to fit the holes (not shown) in the holder.

In the preceding modifications the cross section of the retainer has been rectangular. It will be understood that other shapes of resilient steel and brass can be used, such as round cross sections.

In many respects, the modification of FIGS. 6-10 resembles that of FIGS. 1-5 and the same reference numerals followed by subscript a are used to designate corresponding parts. The retainers of FIGS. 11-17 likewise are similar in many respects to those of preceding modifications, and the same reference numerals followed by subscripts b to h, respectively, are used to designate corresponding parts.

What is claimed is:

1. In combination, an excavating tooth having a proximal portion a distal portion formed with a cutting edge, a tooth holder formed with at least one recess complementary to said proximal portion and opening inward from the forward end of said holder and extending inward from said forward end in a first direction, and a retainer, said retainer having a pair of legs and a connecting portion connecting one end of each said leg, said retainer being formed to resist movement of said legs toward and away from each other, said retainer being slidable in said holder between operative and retracted positions, said holder formed with a pair of first holes and with a pair of second holes extending from the opposite sides of said holder and generally parallel to said first holes, at least one of said second holes intersecting said recess adjacent a margin of said recess, said first and second holes being spaced back from said forward end, said second holes being offset relative to said first holes in a second direction transverse to said first direction, said first and second holes lying in a plane generally perpendicular to said first direction, at least one said first hole intersecting said recess adjacent a margin of said recess, said proximal portion of said tooth formed with at least one notch in one edge thereof and having a shoulder rearward of said notch, at least one leg of said retainer extending into both said first and said second holes and into said notch when said retainer is in operative position and abutting said shoulder to restrain said tooth against dislodgement from said holder, said one leg being movable out of said notch without total removal of said one leg from said holder when said retainer is in retracted postion, said legs biased to diverge from each other so that said legs engage said first holes to resist unintentional movement of said retainer, said one retainer leg being entirely inside said holer when said retainer is in operative position, said retainer being assembled with said holder when either in retracted or in operative position, said holder and said retainer having cooperating means to restrict movement of said retainer to prevent unintentional removal of said retainer beyond said retracted position.

2. The combination of claim 1 in which one wall of at least one of said first-mentioned holes is formed with a protuberance, each leg of said retainer having an upper portion, a lower portion offset laterally relative to said upper portion and a short slanted portion joining said upper and lower portions, said protuberance and said slanted portion comprising said cooperating means, said upper portions reciprocable in said firstmentioned holes, said protuberances engaging at least one said slanted portion to limit outward movement of said reatiner, and said lower portions reciprocable in said second holes, said upper portions fitting into said notch when said retainer is fully inserted in said holder.

3. The combination according to claim 2 in which said proximal portion of said tooth is formed with a slot extending forward from its proximal end to divide said proximal end into two prongs, said holder formed with a web in said recess fitting into said slot, said notch being formed in one of the faces of said prong defining said slot.

4. The combination of claim 2 in which said proximal portion of said tooth is T-shaped in cross-section having a leg and transverse feet, said recess being complementary thereto, said notch being formed in the outside edge of one of said feet of said proximal portion.

5. The combination of claim 2 in which each said hole diverges proceeding outwardly from said recess to permit dirt to escape from said holes.

6. The combination of claim 1 in which said connecting portion extends outside said holder when said retainer is in retracted position and in operative position and in which said holder is formed with 'a protective portuberance on the side of said first-mentioned holes toward said distal portion to protect said retainer against abrasion during digging when said retainer is in operative position;

7. The combination of claim 1 in which the proximal end of said holder is formed with an opening to receive the edge of the equipment to which the holder is attached, a first surface of said holder on one side of said holder formed with two holes shaped to receive a plurality of plow bolts, a second surface of said holder opposite said first surface formed with depressions shaped to receive nuts for said plow bolts with clearance to turn said nuts.

8. The combination of claim 1 in which said tooth at said cutting edge is formed wider than said tooth holder and a plurality of parallel holders are spaced apart side by side with the cutting edges of said teeth forming a substantially continuous blade.

* a= a :u

Claims

2. The combination of claim 1 in which one wall of at least one of said first-mentioned holes is formed with a protuberance, each leg of said retainer having an upper portion, a lower portion offset laterally relative to said upper portion and a short slanted portion joining said upper and lower portions, said protuberance and said slanted portion comprising said cooperating means, said upper portions reciprocable in said first-mentioned holes, said protuberances engaging at least one said slanted portion to limit outward movement of said reatiner, and said lower portions reciprocable in said second holes, said upper portions fitting into said notch when said retainer is fully inserted in said holder.

6. The combination of claim 1 in which said connecting portion extends outside said holder when said retainer is in retracted position and in operative position and in which said holder is formed with a protective portuberanCe on the side of said first-mentioned holes toward said distal portion to protect said retainer against abrasion during digging when said retainer is in operative position.