Thread Pitch Calculator

Pitch, lead, and why they're only the same for single-start threads

Pitch is the distance from one thread crest to the next. Lead is how far the nut or screw actually travels in one full revolution. For an ordinary single-start thread, those are the same distance — but a multi-start thread has two or more separate helical grooves running in parallel, so the part advances by one pitch for each start in a single revolution. Lead = pitch × number of starts, and it's lead, not pitch, that determines how fast a lead screw or multi-start fastener actually advances.

Why multi-start threads exist at all

A multi-start thread gets you a fast lead (quick axial travel per turn) without the deep, coarse, weak thread profile a single-start thread would need to achieve the same lead — that's exactly why fast-advance mechanisms like some lead screws, pen caps, and quick-release fittings use 2 or 3 starts instead of one. The tradeoff is a somewhat harder thread to cut and, for a fastener, a locking feel that behaves differently than an ordinary single-start bolt.

Where this trips people up

If a print or a lead screw spec gives you "lead" but you need "pitch" for a tapping or thread-cutting calculation (or vice versa), mixing them up on a multi-start thread throws every downstream number off by exactly the number of starts. Always confirm which one you actually have before feeding it into the Tap Feed Calculator or a thread-cutting setup, since those calculations want pitch, not lead, per revolution of the actual cutting tool.