They have a ribbed rubber flange that measures about 1-5/8" across the opening

Cycle Electric Inc

Weight: 1 lb 9 oz (708g)

They are quite overbuilt for the application

The technical edge:

Petcock Bung 22mm Long Frisco Chopper Style - Steel - Weld-In for Harley-Davidson Fuel Valves / Petcocks Tire Size_16" They have a ribbed rubberThis weld on, mild steel, extra long Frisco Style steel petcock bung allows you to set a gas tank up Frisco style. Frisco mounted gas tanks have a shallow tunnel and sit up high on the backbone. This bug lets you put your petcock fuel tap at the far rear of the tank for the maximum amount of miles out of that skinny chopper tank. If your fuel valve is midway up the gas tank you can never get all the gasoline to your carburetor! This petcock bung is