Thread pitch

Thread pitch is the distance between adjacent crests (or troughs) of a screw thread, measured along the axis of the fastener. It determines how far a screw advances with each complete revolution.

How it works

A finer pitch means more threads per unit length, which gives a screw finer control and greater clamping force for the same torque. A coarser pitch means fewer, larger threads that are faster to install and more resistant to cross-threading. The pitch is a fundamental parameter in any threaded system — it must match between the bolt and the nut (or tapped hole) for the threads to engage.

Metric pitch

In metric screw threads, pitch is measured directly in millimetres. An M8 × 1.25 bolt has a major diameter of 8 mm and a pitch of 1.25 mm — meaning the bolt advances 1.25 mm per revolution. Common metric pitches: M6 × 1.0, M8 × 1.25, M10 × 1.5, M12 × 1.75.

Imperial pitch (threads per inch)

In imperial (UNC/UNF) threads, pitch is expressed as threads per inch (TPI). A 1/4“-20 bolt has a 1/4-inch diameter and 20 threads per inch. Common imperial pitches: 1/4“-20 (coarse), 1/4“-28 (fine), 3/8“-16 (coarse), 3/8“-24 (fine).

Coarse vs. fine

• Coarse threads (UNC): Faster to install, more resistant to stripping in soft materials, and less likely to cross-thread. Used in general construction and quick assembly.
• Fine threads (UNF): Provide finer adjustment, higher tensile strength, and better vibration resistance. Used in precision machinery, automotive, and aerospace.

Measuring pitch

You can measure thread pitch with a thread gauge (a set of notched blades, each with a different pitch), a ruler (for coarse threads), or a caliper. Matching the gauge to the thread is the quickest way to identify an unknown fastener.