This Steel Short Version gas block is designed for AR-15s with .750 diameter barrels. Three set screws are included.

The gas block fits over the small hole on the top of an AR-15's barrel. It traps some of the excess gas and sends it through a small port, then into a gas tube on top of the barrel, and back into the upper receiver.

The right gas block may not only improve the aesthetics of your build, but it can also improve the function of your rifle. This small AR-15 part can actually reduce recoil and wear, increase reliabiltiy, and give you the option to run suppressed or unsuppressed.