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## Minor Diameter Definition

The minor diameter is the diameter of an imaginary cylinder that touches the smallest diameter of a thread. It depends on the pitch and the thread’s angle.

## Minor Diameter Formula

For a 60° thread (ISO metric and Unified Inch standards), it equals to:

$$D_{Minor} = D_{Nom}\,-\,\frac{5}{8}\,\times\,\sqrt{3}\,\times\,P$$
$$\text {For example, for a UNC 1/4-20 screw, the nominal pitch diameter is:}$$
$$0.25-0.625*0.05 = 0.196^”\,(4.98\,mm)$$

Determining the required Minor Diameter in each case is complicated and depends on the threading standard and the selected class. You can find it out by referring to the thread standards or with our Threading Calculator.