Does the M*Carbo QD single point sling mount hold the tube collar in place?
Only if the collar has two slots in it so it can compress against the receiver halves when sling mount is tightened down like this one from Performance Services LLC.
@Sub2K The QD single point sling mount fits on the receiver tube behind the metal or plastic collar holding it in place. The Dual QD single point sling mount only fits subs with the metal collar like the picture @dave67 shows. You can cut 2 slots in the metal one and save yourself a few bucks.
I assumed the single point sling mount is put on the tube and not the collar.
@Sub2K Ok, I see that now. I was thinking over the collar, so yes the single point sling mount behind the collar would hold it in place.