12-24 UNC 3B Special NoGo Thread Plug member only ( no handle included) for inspecting threads that will receive Helicoil/STI inserts. Tool steel cold stabilized Rc 60-62 light blue optional handles for inch yellow optional handles on metric plugs. NOTE: selection of a 2B or 3B is based on your requirements. a 2B or 3B only effect the pitch diameter of the NoGo plug with a 2B class providing a larger PD on the plug gage. Certificate of Accuracy is included.Click HERE to read about additional Long Form Cert.