Note : this does NOT fit Super 8 projectors.
It does fit regular 8 projectors.
This is a new unused regular 8mm 300 foot film reel.
The diameter of this reel is 5 13/16 inches.
The film is automatically threaded (self threading) into this reel.

Most reels of Ebay are not of this variety.

This is the last few of these I have.

New, unused.