This is a hard-to-find 14/53 (3.78) ring and pinion applicable to all Fiat X1/9s, 128s and Yugo with 4-speed or 5-speed tripode-style transmissions.
This is an aftermaket racing item with low tooth count. It is not an original equipment unit which would have 17/64 teeth. Note, the pinion will NOT work with a stock 53T ring gear.