Thread pitch converter
Convert threads per inch to metric pitch in millimeters and back, for bolts, taps, dies and pipe fittings.
That's 1.27× as coarse as an M6 bolt, while an M10 bolt is 1.18× coarser. Ten millimeters of travel takes about 7.874 turns.
What it means
How coarse is that thread?
Pitch is only half the story: a thread also has a diameter and a flank angle. Metric threads use 60°, as do Unified threads, but British Whitworth uses 55°, so they never interchange.
Every unit
Your pitch in every unit
Learn
Three things worth knowing
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mm pitch = 25.4 ÷ TPI
20 TPI is 1.27 mm. That is tantalizingly close to the metric 1.25 mm pitch, and the two will start together and then bind. Near enough is not enough on a thread.
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Whitworth standardized the screw
Before 1841, every workshop cut its own threads and nothing interchanged. Joseph Whitworth proposed a single standard, which is why threads per inch survived into the metric age.
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Pitch is not lead
On a single-start thread they are equal. On a two-start thread the bolt advances two pitches per turn, so the lead is double the pitch.
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Popular pitch conversions
Background
About thread pitch
Metric threads are specified by the distance between threads: an M8×1.25 bolt advances 1.25 mm per turn. Imperial threads are specified the other way round, by threads per inch, so a ¼-20 bolt has 20 threads in every inch.
The two are reciprocals: pitch in mm = 25.4 ÷ TPI.