Editing Screw thread (section)

====Minor diameter====
[[File:ISO and UTS Thread Dimensions.svg|thumb|The basic profile of all [[UTS thread]]s is the same as that of all [[ISO metric screw thread]]s. Only the commonly used values for ''D''<sub>maj</sub> and ''P'' differ between the two standards.]]

The minor diameter is the lower extreme diameter of the thread. Major diameter minus minor diameter, divided by two, equals the height of the thread. The minor diameter of a nut is its inside diameter. The minor diameter of a bolt can be measured with go/no-go gauges or, directly, with an [[optical comparator]].

As shown in the figure at right, threads of equal pitch and angle that have matching minor diameters, with differing major and pitch diameters, may appear to fit snugly, but only do so radially; threads that have only major diameters matching (not shown) could also be visualized as not allowing radial movement. The reduced ''material condition'', due to the unused spaces between the threads, must be minimized so as not to overly weaken the fasteners.

In order to fit a male thread into the corresponding female thread, the female major and minor diameters must be slightly larger than the male major and minor diameters. However this excess does not usually appear in tables of sizes. Calipers measure the female minor diameter (inside diameter, ID), which is less than caliper measurement of the male major diameter (outside diameter, OD). For example, tables of caliper measurements show  0.69 female ID and 0.75 male OD for the standards of "3/4 SAE J512" threads and "3/4-14 UNF JIS SAE-J514 ISO 8434-2".<ref name="essen">{{Cite web |title=Identifying threads and connectors |url=https://www.essentracomponents.com/en-us/news/product-resources/identifying-threads-and-connectors |access-date=2021-03-05 |website=Essentra Components |language=en-US}}</ref> Note the female threads are identified by the corresponding male major diameter (3/4 inch), not by the actual measurement of the female threads.