Thread Sizes (Dimensions) Explained - Imperial & Metric Thread Sizes Chart

We have discussed the basic thread terms including thread diameters, crest, root and more definitions in the last article. Here we’ll focus on the thread dimensions explain and the standard imperial/metric thread sizes chart.

Thread Sizes Explained - How to Understand/Read Thread Dimensions

Thread sizes are given in nominal sizes, not in actual measurement. For instance, when a screw or bolt measures 5.9mm, it is called a 6mm thread. There are two common methods to write the thread dimensions.

1.Thread sizes in inches are specified by diameter and threads per inch. For example, in the screw size 10-24, the first digit refers to the thread diameter, the and second digit is threads-per-inch (TPI). When the diameter smaller than 1/4”, the value is indicated by a number, like #1 or No.1.

2.Thread sizes in metric are specified by diameter and pitch. The metric thread sizes are generally expressed as M2 × 0.25, the thread diameter is 2mm and pitch is 0.25mm.