It's not a simple bolt, unfortunately. Imagine a bole that instead of a hex head, it has a flat plate at the end, welded on at an angle. This plate sits in the glass frame, underneath the quarterlight glass and glazing seal. To replace it you will need to remove the glass and go in from above.
Making the pivot itself is simple enough with a donr bolt and a strip of mild steel - you will also need to grind a flat in the threaded portion of the bolt.
Installing it is a whole can of worms...