For 1976 & later Mercury/Mariner 3-cyl, 70-90 Hp | 6-cyl, 120-200 Hp | V6, 115-250 Hp outboards.
ID: 2.4375″ | OD: 2.625″ | W: 0.09375″

also crosses with:
Sierra: 18-0858
GLM: 81430
Mallory: 9-76516