I've got some K cylinders that are a little beat up. One has a couple of chips in that collar that extends below the base of the cylinder and slips inside the cases. What is the function of this collar? To get right down to it, would the chips have to be repaired in order to put these jugs back in service? Also, another one has some chips in the fins. I remember from the old board discussions on the repairability of chipped fins, but I seem to remember the important point of "save the broken parts". Well, I don't have the missing parts, but how difficult would it be to fabricate substitutes? And finally, each cylinder has a different casting number. Can anyone tell me if they denote anything, like year, or special model, or anything? The numbers are: 16581-52; 16581-54; 16581-56R. Any thoughts appreciated.