US3836043A

US3836043A - Transit/combination case shock mount arrangement

Info

Publication number: US3836043A
Application number: US00214008A
Authority: US
Inventors: H Levin
Original assignee: Deutsche ITT Industries GmbH
Current assignee: TDK Micronas GmbH; ITT Inc
Priority date: 1971-12-30
Filing date: 1971-12-30
Publication date: 1974-09-17
Anticipated expiration: 1991-09-17

Abstract

This invention comprises several embodiments of multi-functional shock mounts for transit/cases. A resilient (e.g., rubber) molded corner bumper is either bonded to, or captivated along its edges by, a retainer shaped to be demountably coupled to a corner of the case body or cover. The resilient molded portion may additionally be provided with an outer metallic jacket to facilitate sliding and protection thereof, the outer jacket in turn being either bonded to the resilient portion or being captivated along with the rubber by the retainer. The rubber bumper and its associated outer metallic jacket are extended in a cubical shaped center portion beyond the case outer dimensions and hardware, serving to recess same for additional protection. The resilient molded bumper may be in the form of a two or threelegged piece with the legs being retained by the case outer structural members. Additional features such as male and female stacking features, sloped edges to facilitate sliding, and tierings are provided. Shaped coring holes or cast slots or cross ribs in the resilient portion provide for the equivalent spring constant in all dropping and handling modes to be closely equal to the spring constant of the weight of the case and contents on a corner support.

Description

United States Patent 1 1 Levin Sept. 17, 1974 TRANSIT/COMBINATION CASE SHOCK MOUNT ARRANGEMENT [75] Inventor: Herbert L. Levin, Wyckoff, NJ.

[22] Filed: Dec. 30, 1971 [21] Appl. No.: 214,008

217/52, 53, 54; 248/343], 350, 358; 267/137-141; 190/37; 229/14 C, DIG. l; 206/46 FR, 46 FN, 46 M [56] References Cited UNITED STATES PATENTS 163,863 6/1875 Geer 190/37 420,759 2/1890 Arnold.... 190/37 480,709 8/1892 Capitain 190/37 601,831 4/1898 Haydemlr 190/37 1,195,910 8/1916 Cochrane 190/37 1,519,901 12/1924 Boaz et al. .4 220/97 B 2,376,530 5/1945 Dittman 206/46 M 2,724,468 11/1955 Mautner 190/37 3,030,728 4/1962 Wesman..... 229/14 C 3,049,344 8/1962 Hawkins 217/53 UX 3,103,278 9/1963 Kuzma et al. 220/97 R Primary Examiner-William 1. Price Assistant Examiner-Stephen Marcus Attorney, Agent, or Firm-John T. OHalloran; Menotti J. Lombardi, Jr.

[5 7 ABSTRACT This invention comprises several embodiments of multi-functional shock mounts for transit/cases. A resilient (e.g., rubber) molded corner bumper is either bonded to, or captivated along its edges by, a retainer shaped to be demountably coupled to a corner of the case body or cover. The resilient molded portion may additionally be provided with an outer metallic jacket to facilitate sliding and protection thereof, the outer jacket in turn being either bonded to the resilient portion or being captivated along with the rubber by the retainer. The rubber bumper and its associated outer metallic jacket are extended in a cubical shaped center portion beyond the case outer dimensions and hardware, serving to recess same for additional protection. The resilient molded bumper may be in the form of a two or three-legged piece with the legs being retained by the case outer structural members. Additional features such as male and female stacking features, sloped edges to facilitate sliding, and tie-rings are provided. Shaped coring holes or cast slots or cross ribs in the resilient portion provide for the equivalent spring constant in all dropping and handling modes to be closely equal to the spring constant of the weight of the case and contents on a corner support.

28 Claims, 19 Drawing Figures PATENIEDSEPI 11914 3.836.043

SHEET 2 0F 3 I i i E v INVENTOR BYWMXW- AGENT mimosa: nan 3, 35,043

SHEEI 3 [1F 3 CORNER DROP EDGE DROP FACE DROP INVENTOR HERGERT 4. LEI/IN AGENT TRANSIT/COMBINATION CASE SHOCK MOUNT ARRANGEMENT BACKGROUND OF THE INVENTION This invention relates to transit cases, and more particularly to the multi-functional shock mount arrangements for such cases.

In considering, for example, the very stringent requirements of the military as to transit case construction and durability, two of the most serious problems to be overcome in the design of transit cases for military applications are: (1) the capability of the case with a full dummy load to withstand l4 four-foot drops onto a concrete floor, and (2) the capability of the case with internal equipment to withstand 26 four-foot drops onto a plywood floor, and the equipment to operate after testing.

Past results highlighted the problem of damage to existing transit cases, and particularly the corners thereof, resulting from the four-foot drop tests onto concrete or plywood floors. This is particularly noteworthy in view of the fact that the drop tests are considered unanimously by the industry to be destructive tests; that the corners will be deformed; and that military specifications may be interpreted as requiring that there shall be no evidence of damage such as a crushed corner.

Present accepted methods of protecting transit case contents against damage due to shock are: (l) to attach a Transit Frame to the outside of the case, or (2) to place shock mounts between the case and the inner chassis. These two military-approved methods, however, have serious disadvantages:

I. The Transit Frame consists of a rectangular frame within another rectangular frame with rubber bonded between them. The disadvantages thereof are immediately apparent. The pair of frames required for each case is heavy. They occupy a considerable percentage of the total shipping volume. They are expensive, being in the same price range as the case itself. The frame is removable and therefore can be easily lost in the field. The transit frame requires attachment to the case by means of cables and latches.

II. Shock mounts between the case and the inner chassis have the following disadvantages: (a) they occupy the valuable inner volume of the transit case; (b) they are not effective where the front panel of the equipment chassis must be sealed to the transit case to obtain a rain-proof feature; (c) they do not protect the outside of the case, and particularly the comers of the case, against damage due to, for instance, drop tests; and (d) they reduce usable height and width of the chassis front panel.

SUMMARY OF THE INVENTION It is, therefore, the principle object of this invention to solve the problems of protecting a transit case from damage and to reduce shock transmitted to the internal electronic equipment, while at the same time avoid or eliminate the above-indicated drawbacks associated with conventional arrangements.

It is another object of this invention to provide transit case shock mount arrangements, designed to eliminate the problem of corner mounts being ripped off when subjected to sliding, drop tests and rough handling, as occurs, for instance, with arrangements having the individual shock mounts cemented directly to the case.

According to the broader aspects of the invention there is provided a shock mount arrangement for transit type cases comprising a bumper of resilient material mounted at each comer of at least one surface of the case by way of a metallic member, each said bumper being constructed to have cooperating shape with the case corner associated therewith.

A feature of the invention is that each shock mount provided for an exterior corner of the case may be adapted for a stacking mode wherein the shock mount stacking surfaces are provided with male and female stacking features of complementary design.

BRIEF DESCRIPTION OF THE DRAWINGS The above-mentioned and other objects and features, and the invention itself, will become better understood by consideration of the following description when taken in conjunction with the drawings, in which:

FIGS. 1A and 1B are respectively sectional and perspective views of a corner bumper bonded to a metallic corner plate according to the invention;

FIG. 1C diagrammatically illustrates a transit case with cover showing the arrangement of comer bumpers thereon according to the invention;

FIG. 2 is a perspective illustration of one embodiment of resilient corner bumper according to the invention;

FIG. 3A is a perspective view of a corner of a transit case illustrating an outer structural edge member;

FIGS. 38 and 3C illustrate respectively end and perspective views of a second embodiment of resilient corner bumper according to the invention in relation to the case corner and the outer structural edge members as depicted in FIG. 3A;

FIGS. 4A and 4B are respectively diagrammatic side and perspecitve views of a transit case wherein the inventive bumper arrangement is provided with male and female stacking facilities;

FIG. 5 is yet another embodiment of corner bumper according to the invention wherein the molded onepiece resilient portion is comprised of inner and outer portions on either side of a perforated retainer;

FIG. 6 shows a perspective view of a resilient corner bumper with a metallic retainer for demountable coupling to the case corner;

FIG. 7 is a sectional view of a further embodiment of resilient corner bumper wherein the resilient material is provided with a metallic outer jacket;

FIG. 8 shows the embodiment of FIG. 2 in the arrangement illustrated in FIGS. 38 and 3C, with the center portion of the resilient corner bumper being provided with a metallic jacket;

FIG. 9A is a sectional view of a resilient bumper with metallic jacket in arrangement with a metallic retainer demountably coupled to the case;

FIG. 9B is a partial sectional view of an arrangement closely similar to that of FIG. 9A, showing additional hardware and friction reduction facilities;

FIGS. 10A-10C schematically represent the three drop modes required in military case drop tests; and

FIGS. llA-l 1C illustrate three individual means for compensation of unequal forces in a corner bumper arising from the various drop modes.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the figures in general, there is illustrated various embodiments of comer bumpers for transit type cases. In FIG. 1A there is seen a resilient and substantially non-permanently deformable corner bumper 2, such as rubber, bonded to a metallic corner piece or retainer 3, which metallic comer piece 3 is in turn demountably attached to the case 1 by means of for example screws, or alternatively by rivets or welding if other than a demountable facility is desired. It is a direct advantage of this arrangement that the molded rubber corner 2 can be bonded to a small metal corner more strongly and at lower cost than it could be bonded to the case 1 itself. There is also satisfied the military requirements for a reinforced corner on a case. FIG. 1B shows in perspective the relationship between the corner portion 2 and the metal retainer 3 which comprise the inventive corner shock mount. FIG. 1C on the other hand, schematically illustrates the arrangement of the novel corner shock mounts on the transit case body 1 and the cover 4 thereof, wherein the corner bumpers 2 are such as to extend beyond the case hardware and outer dimensions, recessing same for additional protection and reduced shock to the contents of the case. It is to be noted in FIG. 1C that the bumpers on the case body proper are such as to extend further than the corner bumpers associated with the cover portion 4 of the transit case 1. This provision is made in order that the cover does not take the shock from drops on the flat side of the case and serves to protect in genera] the cover portion from rough handling.

An alternative embodiment of the inventive resilient corner shock mount is illustrated in FIG. 2, wherein the resilient portion 12 consists of a center portion and two or three legs extending therefrom perpendicular from one another. The two or three-legged resilient shock mounts may be assembled to the transit case 1 and retained by the case outer structural edge members 5 as illustrated in FIGS. 3A-3C. Whereas FIG. 3A shows the relationship of the outer structural edge members 5 to the case itself, FIG. 38 represents a sectional end illustration of the edge member 5 in relation to the resilient member 12. Each pertinent edge member 5 captivates one of the legs of the molded resilient corner 12 in the space provided between the edge member and the case itself. In a preferred arrangement thereof, the molded corner 12 may have its legs bonded to one of the case edge members 5 and the edge members in turn are demountably coupled to the case at 6. As shown in FIGS. 3B and 3C the molded rubber portion has an extended center portion 12 extending beyond the outer dimensions and hardware of the case. FIG. 3C also illustrates in the resilient molded extended center portion 12 male and female stacking

features

7a and 7b. As indicated, the male stacking feature consists of a substantially circular disc homogeneous with and representing a further extension to the extended center portion 12. The female stacking feature 7b represents a recess of corresponding shape. As represented at 70, the designer has the alternative of providing no stacking feature or alternatively a male or female stacking feature on the third side of the cubical-shaped center extended portion 12' of the comer bumper. Also the male and female stacking facilities are not limited in scope to substantially circular shape. A universal bumper can be made through this invention having stacking features herein indicated and oriented as required on any comer. The arrangement illustrated in FIGS. 2 and 3A-3C particularly eliminates the problem (encountered in the past when rubber corner blocks were cemented t0 the case corners) wherein the rubber corners were ripped off the case when subjected to drops, sliding, and/or rough handling.

FIGS. 4A and 4B, in conjunction with FIG. 3C, further illustrate the stacking

features

7a and 7b molded into the

rubber portion

2, 12 in order to interlock the cases when in a stacked mode, as particularly seen in FIG. 4A. As mentioned hereinbefore, the corner bumpers provided on the covers 4 of the transit cases 1 are extended beyond the case outer dimensions to a lesser degree than the corner bumpers on the case body itself, thereby providing a gap 8 (FIG. 4A) between the respective case covers in the stacked mode in order to facilitate for instance the easy removal of the case covers. The case corners, again, have been extended beyond the case outer skin in order to provide a recess of the hardware, in compliance with military specifications.

A further and alternative embodiment of corner resilient shock mount according to the invention is shown in FIG. 5, wherein the resilient portion is molded around and through a perforated metal corner or retainer 3 so that bonding does not depend upon attachment to the case, and in fact all metal-rubber bonding may be eliminated. Here again, the resilient center portion is raised in order to recess the case hardware, with the trapped or retained portion 2 of the resilient corner being homogeneous therewith through apertures 9 in the retainer 3. The retainer 3 is in turn demountably coupled to the case 1, 4. FIG. 5 also illustrates at 7b the possibility of stacking features as provided hereinbefore; additionally, the resilient bumper portion is provided with sloped edges 10 in order to facilitate sliding.

FIG. 6 illustrates a modification to the arrangement of FIG. 1A, in that rather than having the resilient bumper portion 2 bonded to the metallic retainer 3, the resilient portion is instead in effect clamped to the case by the demountable coupling of the retainer 3 to the case, which serves to captivate the outer edges of the resilient portion 2 between the retainer and the case. Here again bonding of the resilient bumper portion to a metallic piece has been avoided. A preferred altemative embodiment is illustrated in FIGS. 7 and 8 wherein the rubber 2, i.e., the resilient corner portion, contains an outer metallic jacket 11 which facilitates sliding and distributes the shock load over a greater surface of the resilient portion 2. In FIG. 7 the bumper portion 2 is maintained between the metallic jacket 11 and the retainer 3, the jacket 11 in turn being provided with male and female stacking features as represented at 7b and also a sloping or ramp portion 10 to further facilitate sliding and reduction in friction. Metallic jacket 11 is bonded to 2 which in turn is bonded to 3 which is in turn attached to the case. FIG. 8 represents the embodiment of FIG. 3B, modified to include the outer metallic jacket 11. The metal jacket 11 encloses the extended cubical center portion 12' of the resilient bumper 12. In this manner the center extended portion 12 is further protected from drops and rough handling and serves to effect a reduction of friction in a sliding mode. As before, the outer jacket 11 may be provided with the male and female stacking features and corner sloping illustrated in FIG. 7. The outer metal jacket in turn is bonded to the cubical extended center portion 12 or alternatively may be demountably coupled to the case 1.

FIG. 9A shows yet another embodiment according to the invention wherein the cubical shaped extended center portion 2 of the resilient corner bumper is provided with a metallic jacket 11 having outside corners 11' extending beyond the case hardware, wherein the resilient portion 2 and the metal jacket 11 are provided with extensions at 15. The extensions in turn are captivated by a retainer 14 which may be demountably coupled at 6, such that the entire shock mount is retained by captivating the extended portions of the jacket 11 and resilient portion 2 between retainer 14 and the case itself. In this manner, bonding is not required between resilient portion 2 and the case body 1, 4 or the jacket 11. Thus once again there is provided a molded shock absorbing materia sandwiched between a metal outer jacket and the case so that metal-rubber bonding is eliminated. The metallic jacket 11 distributes the shock energy over the outer surface of the shock absorbing material 2. The outer jacket 11, and particularly at ramp 10, (FIG. 98) provides for the equipment to slide more easily on a rough surface without the corners being torn or ripped off.

Additionally included with the metallic retainer 14 on predetermined ones of the various transit case corners, and in particular behind the raised or lip portion thereof which serves to hold the shock mount in place, is a tie-down ring 16, shown particularly in FIG. 9B. A groove or bent channel 16 is provided in the retainer 14 at one corner thereof oriented 45 with respect to the retainer edges. The tie-down ring 16 included at the various corners of the transit/combination cases permits same to be strapped together and/or tied to ground stakes, for example, in a stacked mode for additional stability. In a preferred arrangement the tie-down rings 16, each having the shape of a D, would be provided at the four corners of the case cover 4 for tie-down requirements.

As shown in FIG. 9B, the retainer, in captivating the resilient bumper portion 2 and its outer metallic jacket 11 between it and the case, is either demountably coupled by, for example, screws at 6 or may be mounted by rivets or other suitable means if a removable shock mount facility is not desired. Here again, in view of the holding action of retainer 14, no metal-rubber bonding is required as between the resilient portion 2, the outer jacket 11 or the case itself. The tie-down ring 16 is similarly retained. As may be seen, the retainer depicted in FIGS. 9A and 9B is shaped to permit movement of the outer corner or jacket 1 1 in all directions without metal-to-metal contact between the jacket 11 and the case 1, 4. Also particularly illustrated in FIG. 9B is the angled ramp effect at 10 in the three-piece shock mount (i.e., resilient portion 2, outer jacket 11 and retainer 14).

In all standard drop modes as illustrated in FIGS. l0A-10C a different resilient (rubber) surface is offered as the absorbing medium, while the weight remains constant. One would expect the corner drop to have the greatest shock attenuation of all possible dropping modes, since impact occurs through the least cross-section of the

rubber bumper

2, 12, and therefore the lowest spring constant. The vibration frequency of the weight W on a corner, due to the lowest spring constant, would be the least of all dropping modes. It is expected that if the vibration frequencies in the other dropping modes are higher, as they would be with solid, parallel-piped rubber type sections, less shock attenuation would ensue for these modes. It is therefore desirable to shape the resilient parts so that the equivalent spring constant in all modes is closely equal to the spring constant of the weight on a corner support. The shaping is done by coring holes at slots 18 (FIG. 11A) or casting grooves 19 (FIG. 113) or crossing ribs 20 (FIG. 11C) in the rubber portion to change its crosssection. The optimum cross-section as well as correct material and durometer is determined largely by empirical methods.

In FIG. 11A, cavities or holes are internally provided in rubber bumper portion 2 in the form of elongated and tapered slots 18. In FIG. 118 on the other hand, cavities 19 are in the form of elongated crosssectionally tapered grooves in the under surfaces of the resilient portion 2, whereas in FIG. 11C cavities 20 appear as ribs of substantially constant cross-section and arranged in a crossed pattern on both outer and under surfaces of the rubber bumper 2.

There has been disclosed above several embodiments for multi-functional shock mounts in particular for transit type cases. A resilient (e.g., rubber) molded corner bumper is either bonded to or captivated along its edges by a retainer shaped to be demountably coupled to a comer of the case body or cover. The resilient molded portion may additionally be provided with an outer metallic jacket to facilitate sliding and protection of the rubber bumper, and also to better distribute the shock load throughout the resilient portion, the outer jacket in turn being either bonded to the resilient portion or itself being retained along with the rubber bumper by the retainer. The rubber bumper and its associated outer metallic jacket may be extended in a cubical shaped center portion beyond the case outer dimensions and hardware, serving to recess same for additional protection. The resilient molded bumper may be in the form of a two or three legged piece with the legs being retained by the case outer structural members. Additional features such as male and female stacking features, sloped edges to facilitate sliding and tie-rings have been provided. Shaped coring holes or cast slots or cross ribs in the resilient portion have been provided for the equivalent spring constant in all dropping and handling modes to be closely equal to the spring constant of the weight of the case and contents on a corner support.

While the principles of this invention have been described above in connection with specific apparatus, it is to be understood that this description is made only by way of example and not as a limitation on the scope of the invention as set forth in the objects and features thereof and in the accompanying claims.

I claim:

1. A shock mount arrangement for transit type cases comprising a transit case having a case body and a case cover each having a plurality of comers, a bumper of resilient material mounted at each corner of the case by way of a metallic member, each of said bumpers being constructed to have a cooperating shape with the corner associated therewith, each of said bumpers of said case being provided with male and female stacking features arranged to cooperate with more than two adjacent cases in a stacked mode, said male and female stacking features comprising resilient protrusions extending from and resilient recesses of corresponding shape extending into said bumpers.

2. The arrangement according to claim 1 wherein said bumpers are arranged to extend outward from the case beyond the case outer dimensions and hardware.

3. The arrangement according to claim 2 wherein said bumpers associated with the corners of the case body extend farther out than those associated with the case cover.

4. The arrangement according to claim 1 wherein each of said bumpers is bonded to a metallic corner member arranged to have cooperating design with the associated case corner and bumper, said metallic corner member being in turn demountably coupled to the case.

5. The arrangement according to claim 4 wherein said metallic corner member is adjacent to the associated corner in a form-fitting manner.

6. The arrangement according to claim 4 wherein said bumpers are provided with at least two legs of resilient material homogeneous with and extending from a center portion and wherein said bumper legs are bonded to respective metallic case members each of which in turn is demountably coupled to the case.

7. The arrangement according to claim 5 wherein said resilient legs are bonded to the underside of the edge members which in turn are demountably coupled to the case.

8. The arrangement according to claim 1 wherein the center portion of each resliient bumper is provided with cavities arranged to provide predetermined shock absorption and distribution in accordance with the contact experienced with foreign objects.

9. The arrangement according to claim 8 wherein said cavities are cast elongated and tapered internal slots arranged to provide an equivalent spring constant in all modes of bumper contact of substantially the same as the spring constant resulting from the weight of the case and its contents on a corner.

10. The arrangement according to claim 8 wherein said cavities are in the form of elongated grooves provided on the undersides of the bumper center portion for providing an equivalent spring constant in all modes of bumper contact of substantially the same as the spring constant resulting from the weight of the case and its contents on a corner.

11. The arrangement according to claim 8 wherein said cavities are in the form of crossed ribs on the outer and under surfaces of the bumper center portion for providing an equivalent spring constant in all modes of bumper contact of substantially the same as the spring constant resulting from the weight of the case and its contents on a corner.

12. The arrangement according to claim 1 wherein each of said bumpers is retained by a metallic corner member arranged to have cooperating design with the associated case corner and bumper, said metallic corner member being in turn demountably coupled to the case.

13. The arrangement according to claim 12 wherein said metallic corner member forms an enclosed space with the case and contains a plurality of apertures, and wherein each of said bumpers is constructed with said metallic corner member so as to fill the space provided between said corner member and the case and to be homogeneous by way of said apertures with an outer molded resilient portion which covers said metallic member.

14. The arrangement according to claim 13 wherein said outer resilient corner portion is raised to extend beyond the case outer dimensions and hardware and is of corresponding shape with the corner for providing substantially flat outer contacting surfaces which include said male and female stack features.

15. The arrangement according to claim 12 wherein said bumpers are provided with at least two legs of resilient material homogeneous with and extending from a center portion.

16. The arrangement according to claim 15 wherein said bumper legs are retained by respective metallic case members, each of which is in turn demountably coupled to the case.

17. The arrangement according to claim 16 wherein when the transit case is of the type which includes outer structural edge members, said bumpers are retained in position by the outer structural edge members by way of the captivation thereby of said legs of said bumpers in the space formed between the edge members and case.

18. The arrangement according to claim 17 wherein the center portion of each of said bumpers is extended beyond the outer dimensions of the edge members and case hardware.

19. The arrangement according to claim 18 wherein said corner bumper center portion is substantially cubical in shape with the exposed outer surfaces thereof being provided with male/female stacking facilities.

20. The arrangement according to claim 12 wherein said metallic corner member is coupled to the case by way of a demountable retainer having a lip for retaining said metallic corner member in place.

21. The arrangement according to claim 12 wherein said bumper of resilient material is provided with a metallic jacket of cooperating design on the exterior thereof.

22. The arrangement according to claim 21 wherein said metallic jacket is bonded to said resilient bumper.

23. The arrangement according to claim 21 wherein said bumpers have at least two legs of resilient material homogeneous with and extending from a center portion, with each of said bumper legs being retained by a metallic edge member which is in turn demountably coupled to the case.

24. The arrangement according to claim 21 wherein said metallic jacket is provided with male/female stacking features in the form of protrusions and indentations of corresponding shape positioned in an overlying relationship with said protrusions and said recesses of said bumpers of said case body.

25. The arrangement according to claim 21 wherein said metallic jacket is demountably coupled to the case.

26. The arrangement according to claim 25 wherein said metallic jacket is provided with a ramp-like shape at the edges thereof.

27. The arrangement according to claim 25 wherein said metallic jacket is coupled to the case by way of a demountable retainer having a lip for retaining said metallic jacket in place.

28. A shock mount for exterior corners of a transit case adapted for stacking, comprising a bumper of resilient material mounted to a metallic member shaped to fit each of said exterior corners, each of said bumpers having a stacking surface including one of resilient protrusions extending from and resilient recesses extending into said stacking surface, said protrusions and said recesses having complementary shape.

Claims

1. A shock mount arrangement for transit type cases comprising a transit case having a case body and a case cover each having a plurality of corners, a bumper of resilient material mounted at each corner of the case by way of a metallic member, each of said bumpers being constructed to have a cooperating shape with the corner associated therewith, each of said bumpers of said case being provided with male and female stacking features arranged to cooperate with more than two adjacent cases in a stacked mode, said male and female stacking features comprising resilient protrusions extending from and resilient recesses of corresponding shape extending into said bumpers.