Unified Thread Standard - Basic Profile

Basic Profile

Each thread in the series is characterized by its major diameter D_maj and its pitch, P. UTS threads consist of a symmetric V-shaped thread. In the plane of the thread axis, the flanks of the V have an angle of 60° to each other. The outermost 0.125 and the innermost 0.25 of the height H of the V-shape are cut off from the profile.

The pitch P is the distance between thread peaks. For UTS threads, which are single-start threads, it is equal to the lead, the axial distance that the screw advances during a 360° rotation. UTS threads do not usually use the pitch parameter; instead a parameter known as threads per inch (TPI) is used, which is the reciprocal of the pitch.

The relationship between the height H and the pitch P is found using the following equation:

In an external (male) thread (e.g., on a bolt), the major diameter D_maj and the minor diameter D_min define maximum dimensions of the thread. This means that the external thread must end flat at D_maj, but can be rounded out below the minor diameter D_min. Conversely, in an internal (female) thread (e.g., in a nut), the major and minor diameters are minimum dimensions, therefore the thread profile must end flat at D_min but may be rounded out beyond D_maj.

The minor diameter D_min and effective pitch diameter D_p are derived from the major diameter and pitch as