Interested in this thread because I do have a spare bmx crank from my dumpster find bike. I'd use it on my Diamondback MTB bmx conversion. The DB has a square taper and the BMX is splined.
Is this a feasibe thing to do? I'm sure it'd be more economical to just get a square taper single but a project isn't always cost effective to get desired results
BMX axle set-up like this, 8 splines.

What I've found is I would need something like this...