Helical Beam Shaft Couplings

[Techbuilder]

Hi everyone
I ran into a little problem hopefully someone could help me out.

I have a stepper motor that has a 5mm shaft and I need to connect it to a
3/8-12 threaded rod.

I wanted to use a helical beam shaft coupler but I can't get my hands on a 5mm to 3/8.

So my question to you is if I get 3/16" to 3/8" could I drill the 3/16 to 5mm without damaging the coupler.

Any information would be greatly appreciated

[Bubba]

Personally, I would prefer to chuck up the rod and turn it down to 5mm. This would give more frictional surface to grab onto with the coupler.
Also, drilling can be problematic as not all drills will drill the right size hole and it may not be round!