For before 1960/1973 & later Mercury/Mariner 1-cyl, 4 Hp | 2-cyl, 6-60 Hp | 3-cyl, 50-70 Hp | 4-cyl, 45-80 Hp | 6-cyl, 90-300 Hp | V6, 140-300 Hp outboards.
ID: 0.375″ | OD: 0.5″ | W: 0.0625″

also crosses with:
Sierra: 18-7168-9
GLM: 80120
Mallory: 9-76550