This is a 35mm film takeup spool for old Contax 2/3 and Kiev 2, 3, 4, 4A, 4M and 4AM cameras.

Since this part is removable, it's fairly common to find old Contax/Kiev lacking it. Regular 35mm cassette cores do fit in its place, but film threading will be trickier and proper closing of the camera door will be more difficult.

This is still a work in progress; final assembled part might need some sanding/grinding in order to fit properly inside camera.