Thread pitch converter

This thread pitch converter takes one positive value in TPI, pitch millimetres, pitch inches, threads per centimetre, pitch centimetres, or threads per millimetre and returns the full set of equivalents with fixed decimal rounding for CI-friendly JSON.

TPI, metric pitch, and density units — what each notation means

Threads per millimetre is the reciprocal of pitch_mm and shows up in fine-lead screw and optical-thread math. Send the required field value as a finite positive number and set from to tpi, pitch_mm, pitch_in, tpc, pitch_cm, or threads_per_mm; if you omit from, TPI is assumed because that is the default trade density for this product. Case-insensitive aliases such as threads/in, mm, inch, threads/cm, and t/mm are accepted so free-form forms still resolve. Identical inputs always produce identical JSON because the path is pure reciprocal arithmetic with no network, no random seed, and no wall clock.

How the conversion works and how to read the response

All supported notations share one physical model: a uniform helical pitch with constant crest spacing along the screw axis. The engine normalizes every input to threads per inch using the exact international inch of twenty-five point four millimetres, then expands the full family of outputs. From TPI, pitch_in is one over TPI, pitch_mm is twenty-five point four over TPI, pitch_cm is two point five four over TPI, tpc is TPI divided by two point five four, and threads_per_mm is TPI divided by twenty-five point four. From a metric pitch_mm the engine recovers TPI as twenty-five point four divided by that pitch, then fills the rest. From pitch_in it uses the pure reciprocal; from tpc it multiplies by two point five four; from pitch_cm it divides two point five four by the spacing; from threads_per_mm it multiplies by twenty-five point four. On success the response echoes value and from, then tpi, pitch_mm, pitch_in, tpc, pitch_cm, threads_per_mm, the constant mm_per_inch of twenty-five point four, a formula string for audit logs, method always equal to thread_pitch_exact, and units_supported listing every canonical token. Missing value, non-finite numbers, zero or negative magnitudes, and unknown from tokens all fail with invalid_input and are not charged after the engine rejects the request.

API usage, pricing, shop workflows, and practical limits

Call the free in-browser thread pitch converter when you are reading a tap chart, matching a replacement bolt, or translating a metric pitch callout into TPI for a US stock drawer without opening a spreadsheet. Remember that TPI and metric pitch describe axial crest spacing only—they do not encode thread form, tolerance class, or major diameter—so leave room for standards tables when selecting taps and dies. Send a JSON body with the required finite positive value and optional from defaulting to tpi. Use the prepaid API when a fastener estimator, CNC post-processor, inventory sync, or CAD property panel needs a stable contract under KIT balance at $0.002 per successful item; validation failures never consume balance after the engine rejects the request. Pair this endpoint with length and diameter converters when the next step is major-diameter unit changes, or with general unit tools when drawings mix imperial and metric linear dimensions on the same BOM. Authors shipping SDKs can map tpi and pitch_mm into side-by-side tables that match how imperial and metric shops each talk about the same helix.