This is a capacitor shell used in recapping large old electrolytics as commonly found in 1970's era vintage audio gear.

It can house a modern 8400uf 35v, 18mm diameter by 40mm tall electrolytic capacitor, replacing a 40mm diameter by ~70mm tall 8200uF 35v capacitor with screw terminals on the top.

I just used roughly 3.4mm computer case screws for the screw mount. I reccomend the v2 as it is textured a bit better and has teeth on the top as opposed to the v1 which was my first attempt and a little plain. The v1 lacked screw holes wich made getting the leads up from within the cavity quite a pain