Fuel gauge

Fuel gauge sending unit is not working would like to replace it using existing set up. Looks like a 3/8 female pipe fitting into tank Has anyone replace theirs If so with what. Also would like to confirm the fitting size
Will be setting the tank up to be able to stick it but would like a working sender ( is receiving power just is not registering resistance ).
Jules Verne. 30 U. 428.
GTC Bahamas
Steve Foose. Pittsfield Ma