The SLR Rifleworks Sentry 8 Adjustable Low Profile Gas Block features a mmetering screw and screw bore design, which allows repeatability and reliability only SLR has been able to deliver. Features15-position adjustability from 0 - 0.125" port openingSingle tool click to adjust gas meteringMelonite finish 4140 Precision machined gas blockMelonite finish 4140 Nexturn Swiss precision metering screwStamped Alloy Flat Spring with 1400deg temperMelonite finish 4140 detent plungerTool, roll pin and mounting screws included Note: Needs 1.35" Minimum ID HG (SLR Ion/ Helix HG's OK)