[Grizzman]

Aero receivers, and a few other manufacturers as well, have a threaded hole that allows a plastic tipped set screw to press against the bottom surface of the upper receiver's rear boss. This can be used to eliminate the play between the upper and lower, while still allowing the pin to move without tools.

If you aren't a fan of installing roll pins, Aero's M4E1 receivers use threaded pins for the bolt catch and forward assist retention. This, with the integrated trigger guard, greatly simplifies the assembly process. I don't know of any other forged receivers that have this feature.