A Primer on Typewriter Ribbons & Spools by [[Damon DiMarco]]

Typewriter ribbon is 1/2" wide (12.7mm) which has been standardized as DIN2103.

The DIN 32755 spool, aka a Universal spool, or a Group 1 spool.

Olivetti typewriters use Group 4 spools.

https://www.reddit.com/r/typewriters/comments/18vupsa/database_of_spool_sizes/