Thread Pitch Calculator
Pitch and lead differ the moment you add a start.
Work out Thread Pitch. Pitch and lead differ the moment you add a start. Free, with no account and nothing to install.
Lead — advance per turn
1.25 mm
20.32 TPI · helix angle 3.17° · self-locking
Pitch is the distance between adjacent threads; lead is how far the fastener advances per turn. They are the same only on a single-start thread. A two-start thread advances twice its pitch per turn, which is how fast-action clamps and some lead screws work. The helix angle follows from lead and pitch diameter, and it decides whether a thread self-locks. Below roughly 8° — the friction angle for dry steel on steel — a load cannot drive the thread backwards, which is why ordinary bolts stay put and why a multi-start lead screw needs a brake. Fine threads have a shallower helix, more engagement per unit length and better resistance to vibration loosening, at the cost of being easier to cross-thread and to strip in soft material. Coarse threads are more tolerant of damage and dirt, which is why they dominate general assembly.
How the Thread Pitch Calculator works
Pitch, lead, helix angle, pitch diameter and whether a thread self-locks. Pitch and lead are the same only on a single-start thread, and the difference is what fast-action clamps rely on.
Also known as: difference between pitch and lead · helix angle of a thread · will this thread back off · tpi to metric pitch
Frequently asked questions
What is the difference between pitch and lead?
Pitch is the distance between adjacent threads; lead is how far the fastener advances per turn. They are equal only on a single-start thread — a two-start advances twice its pitch.
What makes a thread self-locking?
A helix angle below the friction angle, around 8° for dry steel on steel. Below that a load cannot drive the thread backwards, which is why ordinary bolts stay put.
Why do lead screws use multi-start threads?
Speed. More starts means more advance per turn without a coarser, weaker thread form — at the cost of self-locking, which is why such screws usually need a brake.
Fine or coarse thread?
Fine threads resist vibration loosening better and have more engagement per unit length; coarse threads tolerate damage and dirt and are far harder to cross-thread. Coarse dominates general assembly for that reason.
How do I convert threads per inch to pitch?
Divide 25.4 by the threads per inch. 20 TPI is 1.27 mm pitch, close to but not the same as M8's 1.25 — which is exactly why the two systems do not interchange.
Put this calculator on your own site
Free to use, on any site, commercial or not. Paste this where you want it to appear. It is a plain iframe, so it works in WordPress, Squarespace, Wix, Webflow, Ghost and anything else that accepts HTML.
<iframe src="https://www.thecalclibrary.com/embed/thread-pitch-calculator" width="100%" height="640" style="border:1px solid #e2e8f0;border-radius:12px" loading="lazy" title="Thread Pitch Calculator"></iframe>
<p style="font:13px/1.5 system-ui,sans-serif;margin:6px 0 0;color:#64748b">Powered by <a href="https://www.thecalclibrary.com/thread-pitch-calculator" style="color:#64748b">Thread Pitch Calculator</a> from The Calc Library</p>The only condition is that the credit line below the frame stays in place. That one line is what pays for the tool being free — it is how anyone else finds it.