The '51 cylinder should have the brake line screwed directly into the head nut (big outlet adapter that screws into end of cylinder) with a 7/16"-24 tube nut. On the '52-'55(1) cylinder, the head nut is tapped 1/2"-20 and will probably have a banjo bolt and fitting, though some may be set up for 1/2"-20 tube nut with a brass tube seat pressed into the head nut.
Joe
