This gasket is a cork/neoprene blend and is intended to be used for the 1928-29 radiator cap only.  We used to sell these for the 1928-29 gas cap and the glass type sediment bowl as well but the ethanol in todays fuels has been causing gasket failures. 

Order A-9173 for 1928-29 gas caps and glass type sediment bowls.  It is made of Viton which is resistant to the ethanol in todays fuels.

2-1/4" OD, 1-35/64" ID, 1/8" thick