The Starrett 6 Inch Screw Pitch Gage contains 30 leaves with 4 to 42 threads per inch. It also features a locking device and 11-1/2 and 27 Pipe Thread Pitches. Starrett screw pitch gages are among the most useful tools in any mechanics' tool box. They quickly determine the pitch of various threads. These gages consist of a substantial steel case with a number of folding leaves at both ends, each leaf having teeth corresponding to a definite pitch, marked on each leaf. They are available in a wide Range of sizes with different numbers of leaves in various pitch Ranges with which to gage. V, Unified, American National 60 degree threads, Whitworth Standard 55 degree threads, International Metric Standard 60 degree threads. English and Metric threads are similar in form, but English threads are described in threads per inch and metric threads by the distance from one crest to the next. All Starrett screw pitch gages (except 476 and 476, which have a positive stop design) feature a locking devices at both ends of the case, so leaves can be securely locked in position for use. Leaves on most gages have a special narrow design, permitting checking internal threads in nuts, etc. as well as external threads.