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). If unable to do so, the thread does not meet the requested standards (=scrap).The scrap side of the thread plug gauge must not be able to be manually turned more than two turns into the cut thread (without using excessive force). If it can be screwed in more, the thread does not meet the requested standards (=scrap).The reference temperature for parts and gauges is 20° Celsius.