Stripped coupler screw head

[Orso]

I have been getting some inconsistent cutting depths lately. 
I took the Z motor cover off and watched the coupler while
the machine was cutting a long flat straight profile and saw the coupler slightly turn. 
So I believe I have traced the problem to the Z axis coupler screw that
attaches to the Z motor. When I first got the machine I managed to strip
the screw head when tightening it down. Now I can't tighten or loosen it. 

I already ordered more couplers but in the meantime I have some hard
deadlines and need the coupler fixed yesterday. 

I'm planning on getting a screw extractor and replacing the set screw. 
I don't want to mess up any of the other coupler screws by removing them.

So I thought I would ask if anyone knew the size of the screw so I could get a replacement?
Thanks
 

[Axiom Tool Group]

Sadly since those screws are supplied with the couplings...I can not confirm the thread with any confidence.