O-Ring -337 V3180 used with Clack WS1 Top of tank to Valve ( WS1 & 1.25 ) o-ring.
Also, the In and Out Head 1190 Clack D1220 New PN D1400.
And the In and Out Head 990S ( MD1226 ).
Also, newer 890S ( MD717105 ) 3/4" In and Out Head since 2011 ( seals to surface, and older versions used 3410381, fits around the threads ).
Dimensions = 3 3/8" O.D. x 3" I.D. x 3/16" thickness