Found a pair of 6 1/4 amp 120v "Fustat" (Buss) screw in fuses. Not the Edison base type, but using the base designed to keep a user from using a too big fuse.
It seems like a odd number, but 6¼A∙120V = 750VA, which is sort of a ‘round’ number. It may have evolved with some UL appliance standard, and not the NEC we’re so familiar with.