i make my own caps by using junk yard lines. just cut the line past where it comes out of the master nuts, then braze the line remnant/nut together. not sure however, if you have access to yard parts. weatherhead fittings, at one time, had adapters that went from the 1/2 & 9/16-20 thread to regular female 3/16" brake line. then all that was required was a pair of male 3/16" brake line plugs to make a cap. edelman also made these adapters. parts stores always had a couple of boxes of these [and other odd ball brake line adapters] behind the counter to help out with emergency repairs.