What is the difference between thread pitch and TPI?

Pitch is the distance in millimetres between one thread crest and the next (metric convention). TPI is how many crests fit in one inch (imperial convention). Both describe the same spacing; convert with P(mm) = 25.4 / TPI.

Why doesn't my measured pitch match any standard size?

A non-matching pitch usually means a fine-thread variant (UNF instead of UNC, or a metric fine pitch instead of coarse), a worn thread, or too few threads counted — re-measure across more threads before assuming it is non-standard.

Is Malta's fastener market metric or imperial?

As an EU member, Malta's fastener market follows the metric ISO 261 standard (M-series). Imperial UNC/UNF threads occasionally appear on older British-legacy plumbing fittings or imported machinery.

Thread Pitch Calculator — Pitch, TPI & Standard Match | Construction Calculators

Thread Pitch Calculator: Convert Between mm Pitch and TPI

Thread pitch is the distance between two adjacent thread crests. Metric threads (ISO 261, the M3-M24 series) state this directly in millimetres per thread; imperial/UTS threads (UNC/UNF, ASME B1.1) use threads per inch (TPI) instead — a count, not a distance. This calculator solves either a measured thread length and thread count, or a known TPI, for the missing value, and reverse-matches the result to the nearest standard metric or UNC designation.

How to use the thread pitch calculator

Choose the solve mode: measure a thread length and count the crests across it, or enter a known TPI directly.
For the length-and-count mode, enter the length you measured and the number of thread crests counted over it, in your chosen unit.
Read off the pitch in mm/thread, the equivalent TPI, and the nearest matching standard designation (e.g. M6 or 1/4"-20 UNC) if the result falls within tolerance of a preset.

The thread pitch formulas

Pitch from a measured length and count: P = L / n. TPI works the other way: TPI = n / L(inches). The two convert via the 25.4 mm/inch constant: P(mm) = 25.4 / TPI, and TPI = 25.4 / P(mm).

Example: 20 mm of thread with 20 crests counted gives P = 20 / 20 = 1.0 mm/thread — matching the M6 coarse pitch, equivalently 25.4 TPI. A 1/4"-20 UNC bolt (20 TPI) converts to (1 / 20) x 25.4 = 1.27 mm, which matches no metric preset, confirming it is an imperial thread.

Tips

Count over as many threads as the fastener allows (10+ where possible) — pitch is a small distance, so counting error shrinks the more threads you span. A thread pitch gauge (a fan of notched blades stamped with mm or TPI values) that seats flush against the crests is faster and more reliable than counting by eye.

In Malta, a standard fastener at this thread pitch typically retails for around €0.13-€2.50 per piece, depending on size, material, and coating.