Dryseal American Standard taper pipe threads. NPTF Class 1 gaging system uses L1 & L3 thread plug gages to gage the internal thread, L1 & L2 ring gages to gage the external threads. The crest and root of the threads are controlled with proper tooling. NPTF Class 2 gaging system uses L1, L2, & L3 thread gages, with the use of Crest and Root Check gages to gage the major and minor diameter of the product.
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