TANK CAP W/GASKET 7911000006630 3 1/2" DIAMETER. was 143-186. CAP. Can also buy the center gasket part # 143-186center. *** Please note some units had a plunger that was about 1/4" longer.. if yours is the longer one you may have to glue a button on the plunger so it will push in farther.. **** #$%