Information contained in this recommended practice is intended for use of pipe manufacturer inspectors@ quality control personnel@ field inspectors@ threading unit operators@ and users and purchasers of oil country tubular goods and line pipe. This publication was prepared under the auspices of the API Subcommittee of Tubular Goods and the Resource Group on Threading and Gauging. As such@ the scope is limited to inspection of API casing@ tubing@ and line pipe connections. However@ the basic techniques of gauge usage apply to any threads for which the thread element specifications are known. Specifically@ this recommended practice was written to supplement and augment the latest editions of API Specifications 5CT and 5L@ which mandate physical and mechanical properties of casing@ tubing@ and line pipe. Additionally@ this recommended practice is designed to be used with the latest edition of API Specification 5B@ Specification for Threading@ Gauging@ and Thread Inspection of Casing@ Tubing@ and Line Pipe Threads . It does not duplicate the massive dimensional tables contained in the latest edition of API Spec 5B. Instead@ it provides instruction in inspection techniques appropriate to comparing the dimension of the product with specified dimensions and tolerances for that product. Accordingly@ the primer can be used for the inspection of API thread elements without direct reference to the latest edition of Spec 5B. In all cases@ the latest edition of Spec 5B takes precedence if a dispute arises between parties. This publication uses photographs to demonstrate the proper use of representative gauges normally used by thread inspectors. Gauges presented are limited to those appropriate to both mill and field use. Thus@ nonportable instruments such as comparators and contour readers are not included. However@ there is no intent to limit the use of such instruments or methods by inspectors.