5/16 18 UNJC 3B Go & NoGo Thread Plug with Taperlock Style W/ Handle tool Steel Rc 60-62 cold stabilized work plug handles can be marked with 15 characters at no additional cost Inch handles will be light blue metric yellow Certificate of Accuracy is included NOTE: selection of a 2B or 3B is based on your requirements. A 2B class plug will have a larger pitch diameter for the NoGoThread member only. The Go member is the same regardless of the class chosen. J convention requires that all Go Ring gages be made with rounded roots and that all gage plugs are marked with this J convention. (mil-S-8879 Aerospace Military & Government) Certificate of Accuracy is included.Click HERE to read about additional Long Form Cert.