The submitter said 3/8x10 didn't fit.
Regular 3/8x10 shafts will thread on most 3/8x10 modified joint pins in my experience. A Revo, Meucci and BeCue CF do fit well. Rhino and SMO CF shafts, for instance, fit but aren't deep enough. They have to be bored out to 38mm or so to work (or at...