The Troy .936 Low Profile Gas Block is made specifically for bull barrel rifles that have a 0.936 gas block seat. The Troy .936 low profile gas block works on both .223" 5.56 and .308 bull barrels and other calibers. An option for users who desire to replace their default gas blocks" or fixed front sight gas blocks to utilize a free float rail system that installs over the gas block. Machined from 4140 pre-hardened steel finished with MIL-STD Manganese Phosphate. Gas tube roll pin not included.