... : API 5B. CSG,LCSG,LP,BCSG,TBG,UPTBG,NC.. API Thread Gauges: Used for gaging API internal and external threads.API Spec ... to 4-1/2"All gages are produced in Drake thread grinding machine, and checked by B&S CMM and master ... , we will response you at the first time! API 5B Thread Gauges