UPPER RECEIVER DETAILS:
MIL-Spec inner dimension measures at 1.000 -0.0/+0.002"
Thermal Fit inner dimension measures at .997 -0.0/+0.001" and requires the application of heat in order to provide a solid mate to the recommended barrel extension. By heat we mean more than granny's hair dryer.
-For Use with M4 Barrel extensions-Assembled Upper Receivers come with ejection port cover and forward assist installed
**FFL Required Before Shipping.**
*** We recommend gunsmith installation for all of our parts. We cannot warranty items damaged by improper installation.
