Pipe threads (PTF) are larger in diameter than most UNF or SAE-LT threads and also provide additional strength. PTF threads have a taper like SAE-LT threads to provide a 1"leakproof1" installation. These threads are designated by nominal pipe diameter. The 1/8 PTF thread is actually about 3/81" diameter, and the 1/4 PTF thread is about 1/21" diameter. A tapped hole is required for installation. PTF fittings are used most often in construction and in the agriculgural industry where heavy machinery is required. Maximum pressure is 8,000 PSI. All zinc dichromate fittings minimum 96 hours to red rust. All zinc fittings case hardened to Vickers HV1 or 83 min Rockwell 15N.

For 1/4” - 28 thread self-tapping now needed on many parts of new cars. Can be threaded into .226 to .300 diameter hole. Cuts its own thread.