If you reload your own 35mm film cassettes from a bulk loader, then you're going to need some of these !
This is an empty Ilford vintage film canister from the 1980s & 90s that originally contained Ilford's FP4 black & white 35mm film, but unlike all their current 35mm film canisters - which are now 'crimped' at either end to prevent the caps coming off - this one you can pop off the end caps to re-install / re-load more film from a bulk reel with a loader.
Clever, huh ?