Do you have size of joint on the BEM and ebony? is it close to .840?
I measured it 4 times cause I don't like scratching the surface: .841; .840; .842; & .841 so I would say yes, it is close to .840

The pin is 3/8x10, will any aftermarket shaft with 3/8x10 fit?
Dajo
Yes (but it's hard to say "any", you never know). I screwed in the following shafts to retest it: McDermott, Carmeli, Coker, Schrager & Judd. The Judd was a little tight because he treats his threads a certain way to make sure they fit snugly, but it went on. All others were no problem.
Thanks for your interest.
Dave