The Forster 7.62x39 GO Headspace Gauge is a precision gunsmithing tool manufactured to SAAMI specifications with exacting standards for accurate testing of rifle chamber dimensions.7.62x39 caliber GO headspace gauge1.252" SAAMI specification measurementPrecision-machined steel constructionTests chamber acceptance of SAAMI-spec ammunitionEssential tool for safe rifle chamberingProfessional gunsmith qualityIf a rifle closes on this GO gauge the chamber will safely accept any ammunition manufactured within SAAMI industry standards. Essential for gunsmiths ensuring proper headspace to prevent dangerous excessive chamber dimensions that could cause brass rupture and gas blowback.