Backs for Nikon F100 film cameras. They have a weak point - the catches are thin plastic, and will eventually break off, as I discovered a few years ago.

Lower one is the original, also here;
Middle was a bare back that I fitted all the bits on from the original, except the hinges, and I couldn't find replacements for those;
The top one, I must have bought two of (and forgot that I had) via Nikon UK. Only needed to swap the film pressure plate over to a new one of the pair bought, and then used that on my camera.

Recently bought a cheap F100 that wasn't working, was missing the battery holder, and had a back with both catches broken. Put my original camera's battery pack in, and everything seems to work okay. Found that B&H in the USA had brand new battery packs available (cheaper than used ones!) and ordered one. That spare back at the top may be deployed sometime next year for a full test.