VCOIL Plug Gauge (D/E) - UNF (STI) - Heli Coil Gauge - Right Hand - 3B - 5/8 x 18Helicoil gauges are manufactured and assessed in accordance with the relevant ANSI standards, specifically those defined by the American National Standards Institute ASME thread system. A thread limit plug gauge is a combination of go plug gauge and no go plug gauge. The scrap side of the thread plug gauge is marked with a red ring. The go end of the thread plug gauge must screw into the thread cut into a part by hand (without using excessive force).