{"id":100259,"date":"2026-02-15T20:30:16","date_gmt":"2026-02-15T20:30:16","guid":{"rendered":"https:\/\/vibromera.eu\/?post_type=calculator&#038;p=100259"},"modified":"2026-07-15T20:09:53","modified_gmt":"2026-07-15T20:09:53","slug":"thread-size-converter","status":"publish","type":"calculator","link":"https:\/\/vibromera.eu\/hr\/calculators\/thread-size-converter\/","title":{"rendered":"Controlled Thread Geometry Unit Converter"},"content":{"rendered":"<div id=\"th-tool\" class=\"th-shell\">\n<style>\n    #th-tool{--ink:#172535;--muted:#52657a;--line:#d5e0e8;--soft:#f3f7fa;--accent:#a93d17;--accent2:#7c2b10;--warn:#fff1e9;--ok:#136c42;font:16px\/1.55 system-ui,-apple-system,\"Segoe UI\",sans-serif;color:var(--ink);max-width:1180px;margin:0 auto;background:#fff}\n    #th-tool *{box-sizing:border-box}#th-tool .th-hero{text-align:center;padding:52px 24px 42px}#th-tool .th-kicker{margin:0 0 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.th-rvalue{font-size:21px;font-weight:820;overflow-wrap:anywhere;margin-top:4px}#th-tool .th-note,#th-tool .th-record{border:1px solid var(--line);border-radius:10px;padding:13px;margin-top:12px}#th-tool .th-record{font-size:13px;color:var(--muted)}\n    #th-tool .th-formula{font:700 16px\/1.75 ui-monospace,SFMono-Regular,Consolas,monospace;background:var(--soft);border:1px solid var(--line);border-radius:10px;padding:16px;overflow-x:auto}#th-tool .th-small{font-size:13px;color:var(--muted)}#th-tool .th-list{padding-left:21px}#th-tool .th-list li{margin:9px 0}#th-tool .th-source{border-top:1px solid var(--line);padding:16px 0}#th-tool .th-source:first-of-type{border-top:0;padding-top:0}#th-tool .th-source a{color:var(--accent2);font-weight:800}#th-tool .th-source p{margin:3px 0;color:var(--muted);font-size:14px}#th-tool .th-footer{text-align:center;color:var(--muted);font-size:13px;padding:8px 20px 34px}\n    @media(max-width:700px){#th-tool .th-hero{padding:38px 18px 32px}#th-tool .th-sub{font-size:16px}#th-tool .th-card{padding:20px;margin-left:0;margin-right:0}#th-tool .th-grid,#th-tool .th-results{grid-template-columns:1fr}#th-tool .th-wide{grid-column:auto}}@media(max-width:430px){#th-tool h1{font-size:31px}#th-tool .th-actions button{width:100%}}\n  <\/style>\n<header class=\"th-hero\">\n<p class=\"th-kicker\">Unit conversion, not thread substitution<\/p>\n<h1>Thread Geometry Unit Converter<\/h1>\n<p class=\"th-sub\">Convert the nominal diameter and axial pitch of one documented thread between millimetres, inches and threads per inch. The result does not select a mating thread or declare different thread systems interchangeable.<\/p>\n<div class=\"th-badges\"><span class=\"th-badge\">Exact inch conversion<\/span><span class=\"th-badge\">Signed-off input record<\/span><span class=\"th-badge\">No closest equivalent<\/span><span class=\"th-badge\">No strength claim<\/span><\/div>\n<\/header>\n<section class=\"th-card\" aria-labelledby=\"th-calc-title\">\n<h2 id=\"th-calc-title\">Controlled-input conversion<\/h2>\n<div class=\"th-warning\"><strong>Do not use converted nominal diameter and pitch alone to select a replacement or mating fastener.<\/strong> Compatibility also depends on the complete thread standard and designation, profile, tolerance class or fit, allowance, pitch diameter and crest\/root limits, taper or parallel form, handedness, number of starts, coating and verified gauging.<\/div>\n<form id=\"th-form\" novalidate autocomplete=\"off\">\n<div class=\"th-grid\">\n        <label class=\"th-wide\" for=\"th-system\">Declared thread system<span class=\"th-help\">Used only to identify the record boundary; it does not change the unit arithmetic<\/span><select id=\"th-system\"><option value=\"\" selected disabled>Select the documented system<\/option><option value=\"iso\">ISO general-purpose metric thread<\/option><option value=\"unified\">Unified inch thread (UN family)<\/option><option value=\"whitworth\">Parallel Whitworth-form thread<\/option><\/select><\/label><br \/>\n        <label for=\"th-diameter\">Nominal diameter<span class=\"th-help\">Positive decimal; inch input may also be a fraction such as 1\/2 or 1-1\/4<\/span><input id=\"th-diameter\" type=\"text\" inputmode=\"decimal\" maxlength=\"64\" aria-describedby=\"th-calc-title\"><\/label><br \/>\n        <label for=\"th-diameter-unit\">Diameter unit<span class=\"th-help\">Unit of the entered nominal diameter<\/span><select id=\"th-diameter-unit\"><option value=\"\" selected disabled>Select diameter unit<\/option><option value=\"mm\">millimetres (mm)<\/option><option value=\"in\">inches (in)<\/option><\/select><\/label><br \/>\n        <label for=\"th-pitch\">Axial pitch or TPI<span class=\"th-help\">Positive plain decimal; pitch is the axial spacing for this recorded thread<\/span><input id=\"th-pitch\" type=\"text\" inputmode=\"decimal\" maxlength=\"64\"><\/label><br \/>\n        <label for=\"th-pitch-unit\">Pitch input unit<span class=\"th-help\">Use mm for axial pitch or TPI for threads per inch<\/span><select id=\"th-pitch-unit\"><option value=\"\" selected disabled>Select pitch unit<\/option><option value=\"mm\">pitch in millimetres<\/option><option value=\"tpi\">threads per inch (TPI)<\/option><\/select><\/label><br \/>\n        <label class=\"th-wide\" for=\"th-source\">Identification and source record<span class=\"th-help\">Record drawing\/specification revision, gauge or measurement basis, complete designation and condition<\/span><textarea id=\"th-source\" maxlength=\"500\"><\/textarea><\/label><br \/>\n        <label class=\"th-check th-wide\" for=\"th-confirm-geometry\"><input id=\"th-confirm-geometry\" type=\"checkbox\"><span>I confirm that the nominal diameter and axial pitch\/TPI refer to the same documented thread and that their units are known.<\/span><\/label><br \/>\n        <label class=\"th-check th-wide\" for=\"th-confirm-boundary\"><input id=\"th-confirm-boundary\" type=\"checkbox\"><span>I understand that this is unit conversion only and does not establish fit, interchangeability, strength, proof load, tightening torque or vibration resistance.<\/span><\/label>\n      <\/div>\n<div class=\"th-actions\"><button class=\"th-primary\" type=\"submit\">Convert documented geometry<\/button><button class=\"th-clear\" id=\"th-clear\" type=\"reset\">Clear<\/button><\/div>\n<div class=\"th-status\" id=\"th-status\" role=\"status\" aria-live=\"polite\"><\/div>\n<div class=\"th-output\" id=\"th-output\" data-visible=\"false\" aria-live=\"polite\">\n<h3>Unit-conversion result<\/h3>\n<div class=\"th-results\">\n<div class=\"th-result\">\n<div class=\"th-rlabel\">Declared system<\/div>\n<div class=\"th-rvalue\" id=\"th-r-system\">\u2014<\/div>\n<\/div>\n<div class=\"th-result\">\n<div class=\"th-rlabel\">Nominal diameter<\/div>\n<div class=\"th-rvalue\" id=\"th-r-diameter\">\u2014<\/div>\n<\/div>\n<div class=\"th-result\">\n<div class=\"th-rlabel\">Axial pitch<\/div>\n<div class=\"th-rvalue\" id=\"th-r-pitch\">\u2014<\/div>\n<\/div>\n<div class=\"th-result\">\n<div class=\"th-rlabel\">Threads per inch<\/div>\n<div class=\"th-rvalue\" id=\"th-r-tpi\">\u2014<\/div>\n<\/div>\n<div class=\"th-result\">\n<div class=\"th-rlabel\">Diameter-to-pitch ratio d\/P<\/div>\n<div class=\"th-rvalue\" id=\"th-r-ratio\">\u2014<\/div>\n<\/div><\/div>\n<div class=\"th-note\" id=\"th-r-note\"><\/div>\n<div class=\"th-record\" id=\"th-r-record\"><\/div>\n<\/p><\/div>\n<\/p><\/form>\n<\/section>\n<section class=\"th-card\" aria-labelledby=\"th-model-title\">\n<h2 id=\"th-model-title\">Arithmetic and units<\/h2>\n<div class=\"th-formula\">d(mm) = 25.4 \u00d7 d(in)<br \/>P(mm) = 25.4 \/ TPI<br \/>TPI = 25.4 \/ P(mm)<br \/>d\/P = d(mm) \/ P(mm)<\/div>\n<p>NIST lists 1 inch = 2.54 centimetres exactly, so 1 inch = 25.4 millimetres exactly. The same exact factor converts an inch-based axial repeat into millimetres.<\/p>\n<p class=\"th-small\">The dimensionless d\/P ratio is only a geometry descriptor. No basic, pitch, minor or tensile-stress area is inferred; those quantities require the applicable profile, formula, class and controlled standard data.<\/p>\n<\/section>\n<section class=\"th-card\" aria-labelledby=\"th-boundary-title\">\n<h2 id=\"th-boundary-title\">Standards boundary<\/h2>\n<ul class=\"th-list\">\n<li>ISO 261:1998, Edition 2 remains current after confirmation in 2024 and defines the general plan for ISO general-purpose metric threads. ISO 262:2023, Edition 3 selects commercial metric fastener diameter\/pitch combinations from that plan.<\/li>\n<li>ASME B1.1-2024 specifies unified inch thread form, series, class, allowance, tolerance and designation. This page does not reproduce its proprietary tables or declare a metric\/Whitworth replacement.<\/li>\n<li>BS 84:2007 is the current BSI specification for parallel Whitworth-form threads and replaced withdrawn BS 84:1956. BSW is not BSP, and neither is inferred from diameter and TPI alone.<\/li>\n<li>Pitch choice alone does not guarantee resistance to vibration loosening. Active NASA-STD-5020B, revalidated in 2026, addresses preload, friction, cyclic slip, dynamic loads and locking features as joint-level factors.<\/li>\n<\/ul>\n<\/section>\n<section class=\"th-card\" aria-labelledby=\"th-evidence-title\">\n<h2 id=\"th-evidence-title\">Official evidence<\/h2>\n<div class=\"th-source\"><a href=\"https:\/\/www.iso.org\/standard\/4165.html\" target=\"_blank\" rel=\"noopener\">ISO 261:1998, Edition 2 (confirmed 2024)<\/a><\/p>\n<p>Official current-status and scope page for the metric general plan.<\/p>\n<\/div>\n<div class=\"th-source\"><a href=\"https:\/\/www.iso.org\/standard\/85105.html\" target=\"_blank\" rel=\"noopener\">ISO 262:2023, Edition 3<\/a><\/p>\n<p>Official page for selected commercial metric fastener sizes from ISO 261; it replaces ISO 262:1998.<\/p>\n<\/div>\n<div class=\"th-source\"><a href=\"https:\/\/www.asme.org\/codes-standards\/find-codes-standards\/b1-1-unified-inch-screw-threads-un-unr-thread-form\" target=\"_blank\" rel=\"noopener\">ASME B1.1-2024<\/a><\/p>\n<p>Official scope and current-edition page for unified inch threads.<\/p>\n<\/div>\n<div class=\"th-source\"><a href=\"https:\/\/knowledge.bsigroup.com\/products\/parallel-screw-threads-of-whitworth-form-requirements\" target=\"_blank\" rel=\"noopener\">BS 84:2007<\/a><\/p>\n<p>Official BSI current-status page for parallel Whitworth-form thread requirements.<\/p>\n<\/div>\n<div class=\"th-source\"><a href=\"https:\/\/www.nist.gov\/pml\/owm\/si-units-length\" target=\"_blank\" rel=\"noopener\">NIST SI Units \u2013 Length (updated 2025)<\/a><\/p>\n<p>Official NIST page stating that the standard inch is exactly equivalent to 25.4 mm.<\/p>\n<\/div>\n<div class=\"th-source\"><a href=\"https:\/\/standards.nasa.gov\/standard\/nasa\/nasa-std-5020\" target=\"_blank\" rel=\"noopener\">NASA-STD-5020B (active; revalidated 2026)<\/a><\/p>\n<p>Official fastening-system requirements and joint-locking guidance for dynamic environments.<\/p>\n<\/div>\n<\/section>\n<footer class=\"th-footer\">Vibromera geometry reference \u00b7 No thread selection, fit or strength decision<\/footer>\n<p>  <script>\n  (function(){'use strict';\n    var root=document.getElementById('th-tool'),form=document.getElementById('th-form'),output=document.getElementById('th-output'),status=document.getElementById('th-status');\n    var labels={iso:'ISO general-purpose metric',unified:'Unified inch (UN family)',whitworth:'Parallel Whitworth form'};\n    function byId(id){return document.getElementById(id)}\n    function fail(message){status.textContent=message;status.dataset.kind='error';output.dataset.visible='false';['th-r-system','th-r-diameter','th-r-pitch','th-r-tpi','th-r-ratio'].forEach(function(id){byId(id).textContent='\u2014'});byId('th-r-note').textContent='';byId('th-r-record').textContent=''}\n    function plain(raw,label){var s=String(raw).trim();if(!s||s.length>64||!\/^[+]?(?:\\d+(?:[.,]\\d*)?|[.,]\\d+)$\/.test(s))throw new Error('Enter '+label+' as one positive plain decimal.');var value=Number(s.replace(',','.'));if(!Number.isFinite(value)||value<=0)throw new Error(label.charAt(0).toUpperCase()+label.slice(1)+' must be greater than 0.');return value}\n    function diameter(raw,unit){var s=String(raw).trim();if(unit!=='in')return plain(s,'nominal diameter');var mixed=s.match(\/^(\\d+)(?:-|\\s+)(\\d+)\\\/(\\d+)$\/),fraction=s.match(\/^(\\d+)\\\/(\\d+)$\/),value;if(mixed){var whole=Number(mixed[1]),num=Number(mixed[2]),den=Number(mixed[3]);if(den===0||num===0||num>=den)throw new Error('Enter the inch diameter as a valid decimal or fraction.');value=whole+num\/den}else if(fraction){var n=Number(fraction[1]),d=Number(fraction[2]);if(d===0||n===0)throw new Error('Enter the inch diameter as a valid decimal or fraction.');value=n\/d}else value=plain(s,'nominal diameter');if(!Number.isFinite(value)||value<=0)throw new Error('Nominal diameter must be greater than 0.');return value}\n    function record(raw,label){var s=String(raw).trim();if(s.length<3||s.length>500||\/[\\u0000-\\u0008\\u000B\\u000C\\u000E-\\u001F\\u007F]\/.test(s))throw new Error('Describe the '+label+' in 3\u2013500 printable characters.');return s}\n    function fmt(value){if(Math.abs(value)<1e-14)return'0';return Number(value.toPrecision(12)).toString()}\n    form.addEventListener('submit',function(event){event.preventDefault();try{var system=byId('th-system').value,dUnit=byId('th-diameter-unit').value,pUnit=byId('th-pitch-unit').value;if(!labels[system])throw new Error('Select the documented thread system.');if(dUnit!=='mm'&&dUnit!=='in')throw new Error('Select the diameter unit.');if(pUnit!=='mm'&&pUnit!=='tpi')throw new Error('Select the pitch input unit.');var dInput=diameter(byId('th-diameter').value,dUnit),pInput=plain(byId('th-pitch').value,pUnit==='mm'?'axial pitch':'TPI'),source=record(byId('th-source').value,'identification and source record');if(!byId('th-confirm-geometry').checked)throw new Error('Confirm that both geometry inputs describe the same documented thread.');if(!byId('th-confirm-boundary').checked)throw new Error('Confirm the unit-conversion and non-interchangeability boundary.');var dmm=dUnit==='in'?dInput*25.4:dInput,pmm=pUnit==='tpi'?25.4\/pInput:pInput,tpi=25.4\/pmm;if(!Number.isFinite(dmm)||!Number.isFinite(pmm)||!Number.isFinite(tpi)||dmm<=0||pmm<=0||dmm>1000000||pmm>1000000||tpi>1000000000)throw new Error('Converted geometry is outside the supported positive finite range.');var ratio=dmm\/pmm;if(!Number.isFinite(ratio)||ratio>1000000000000)throw new Error('The diameter-to-pitch ratio is outside the supported finite range.');byId('th-r-system').textContent=labels[system];byId('th-r-diameter').textContent=fmt(dmm)+' mm ('+fmt(dmm\/25.4)+' in)';byId('th-r-pitch').textContent=fmt(pmm)+' mm ('+fmt(pmm\/25.4)+' in)';byId('th-r-tpi').textContent=fmt(tpi)+' TPI';byId('th-r-ratio').textContent=fmt(ratio);byId('th-r-note').textContent='Unit conversion of one declared thread only. 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