This little assembly is engineered to replace an original Olivetti Lettera 31 / DORA typewriter ribbon spool. Please note that it probably also fits a lot of other Olivetti modes or similar branded typewriters as well (Olivetti has a LOT of rebranded variants out there).

Note that this design imitates the Corona 3 ribbon retaining mechanism. The original Olivetti spool design is needlessly complex in terms of 3D printing, so these will not pass for actual, authentic replacements. Duh.

Print the top and bottom flanges, loop the end of the ink ribbon around the inner center of the bottom flange, secure it tightly with the clip, then assemble the top flange.

NOTE that the top flange is actually the bottom of the assembled spool, as that side contains the recessed space necessary to screw the spool retainment nut on (assuming you have the original spool nuts). Keep this orientation in mind when wrapping your ribbons the correct way around.