Described herein are end caps which, as well as being connectible to the ends of the canisters, have recesses so that the end caps, having been removed from the canisters, can do {HEAD ~ double duty} engaged between the sides of the canisters to support and space {TAIL ~ the canisters} in a stack formation 
Described herein are end caps which , as well as being connectible to the ends of the canisters , have recesses so that the end caps , having been removed from the canisters , can do { HEAD ~ double duty } engaged between the sides of the canisters to support and space { TAIL ~ the canisters } in a stack formation
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