1TPI

1TPI is a shorthand notation for one thread per inch, used in imperial screw thread measurements to denote thread pitch. It indicates how densely the threads are spaced along the screw or bolt, measured as the distance between corresponding points on adjacent threads along the axis. In practice, TPI is specified together with the nominal diameter to identify a fastener within standards such as the Unified Thread Standard (UTS). A designation of 1 TPI without a diameter is incomplete, since many diameters can have a 1 TPI pitch; most common fasteners are specified by both diameter and TPI (for example, 1/4-20 UNC).

A 1 TPI thread is extremely coarse and is uncommon for small fasteners. It may be found on large-diameter bolts or in specialized applications where quick assembly or deep thread engagement is prioritized, though it offers less load-bearing surface and stiffness compared with finer pitches.

The term 1TPI can also appear in other contexts that use the acronym TPI, such as teeth per inch in saw blades, where 1 TPI would indicate an unusually coarse blade suitable for very soft materials. In screw-thread discussions, however, 1 TPI refers to an imperial pitch and is a rare, specialized pitch within modern fastener practice.

See also: threads per inch, screw thread, standard thread systems, imperial units.