This gas block replaces your existing front sight to provide a simple, low profile design that can be used to mount a rifle length forearm to a carbine length barrel. It is mounted by the use of two clamping screws. Compatible with 0.750" barrels. Made in the USA. Note: Gas tube roll pin is not included.This gas block replaces your existing front sight to provide a simple, low profile design that can be used to mount a rifle length forearm to a carbine length barrel. It is mounted by the use of two clamping screws.