These are simple battery spacers that push-fit onto the positive button terminal on the top of a C-cell battery to avoid shorts and minimize lateral cell wobble when in a battery pack.
I used four of these to create a DIY four-cell stick NiMH battery pack for a portable oscilloscope with an old fried NiCd pack. I hope someone finds these useful for their project!
DISCLAIMER: I do not recommend soldering to bare battery terminals! Spend a couple bucks more and get the tabbed versions of the cell so you aren't soldering on something susceptible to thermal runaway.
The author marked this model as their own original creation.