Thanks for the advice, I can measure the pitch of the thread in the cylinder from the “adapter”. The best I can measure it, is for the old tap – O.D. = 0.375″ core ~ 0.33″ pitch ~ 0.039″ and for the “adaptor” that screws into the cylinder O.D. = 0.427″ core ~ 0.36″ pitch ~ 0.053″. Does that help ?