{"id":176249,"date":"2025-11-22T22:00:00","date_gmt":"2025-11-22T19:00:00","guid":{"rendered":"https:\/\/bukvaved.top\/v-chjom-raznica-mezhdu-metricheskoj-i-djujmovoj-rezboj\/"},"modified":"2026-10-28T16:29:04","modified_gmt":"2026-10-28T13:29:04","slug":"what-is-the-difference-between-metric-and-dc-threads","status":"publish","type":"post","link":"https:\/\/bukvaved.top\/en\/v-chjom-raznica-mezhdu-metricheskoj-i-djujmovoj-rezboj\/","title":{"rendered":"What is the difference between metric and inch threads?"},"content":{"rendered":"<p><strong>Metric threads differ from inch threads in their units of measurement and description: in metric threads, the diameter and pitch are specified in millimeters (e.g. M10\u00d71.5), while in inch threads, the diameter is specified in inches and the pitch is the number of threads per inch (e.g. 1\/4\u2033-20 UNC).<\/strong> The thread angle can also vary\u2014metric threads are always 60\u00b0, while imperial threads are either 60\u00b0 (American UNC\/UNF, NPT) or 55\u00b0 (British Whitworth, including the popular G-thread for pipe). Therefore, screws and nuts from both systems are usually not compatible.<\/p>\n<p> To sum it up<\/p>\n<ul>\n<li> <strong>Units of measurement:<\/strong> Metric \u2013 millimeters; Imperial \u2013 inches (1 inch = 25.4 mm).<\/li>\n<li> <strong>Thread pitch:<\/strong> In the metric system, the distance between threads in mm; in the inch system, the number of threads per inch (TPI).<\/li>\n<li> <strong>Profile angle:<\/strong> metric 60\u00b0; inch 60\u00b0 (UNC, UNF, NPT) or 55\u00b0 (Whitworth, G and R pipes).<\/li>\n<li> <strong>Plumbing:<\/strong> A 1\/2&quot; thread is actually approximately 21mm in diameter - the name doesn&#039;t match the size.<\/li>\n<\/ul>\n<h2> Metric threads \u2013 designations and construction<\/h2>\n<p> <strong>ISO metric thread<\/strong> \u2014 is the most common fastener thread in the world, used in screws, bolts and nuts. It has <strong>triangular profile with an angle of 60\u00b0<\/strong> , and all dimensions are given in millimeters.<\/p>\n<p> The designation consists of a letter <strong>M<\/strong> and the nominal diameter in mm. For each diameter there is <strong>standard<\/strong> (coarse) thread pitch that drops down \u2013 for example, M10 is a thread with a diameter of 10 mm and a pitch of 1.5 mm. <strong>Small<\/strong> Threads are designated by their pitch, such as M10\u00d71.25 or M10\u00d71. Fine pitch is used when the connection requires higher pressure or when the wall is thin.<\/p>\n<h2> Inch threads - several different systems<\/h2>\n<p> \u00ab&quot;Inch thread&quot; is not a single standard, but a whole family. What they have in common is that dimensions are specified in inches, and the thread pitch is <strong>in threads per inch<\/strong> (TPI). The most important types are:<\/p>\n<ul>\n<li> <strong>UNC and UNF<\/strong> (Unified) \u2013 American fasteners with a 60\u00b0 thread, produced in coarse (UNC) and fine (UNF) versions. The designation 1\/4\u2033-20 UNC means a diameter of 1\/4 inch and 20 threads per inch.<\/li>\n<li> <strong>BSW<\/strong> (Whitworth) - a historical British fastener thread with a 55\u00b0 angle and rounded ends.<\/li>\n<li> <strong>Whitworth carving<\/strong> - cylindrical <strong>G<\/strong> (ISO 228 standard) and conical <strong>R<\/strong> (ISO standard 7). It has a 55\u00b0 angle and is an inch thread used in Polish water supply and heating systems.<\/li>\n<li> <strong>NPT<\/strong> \u2013 American tapered pipe thread with an angle of 60\u00b0.<\/li>\n<\/ul>\n<h3> Trap: In hydraulics, an inch is not 25.4 mm.<\/h3>\n<p> In threaded connections, the number in the designation indicates <strong>nominal pipe size<\/strong> , and not by thread diameter. For example, <strong>G 1\/2 thread<\/strong> It has an outside diameter of 20.955 mm and 14 threads per inch, although half an inch is only 12.7 mm. Therefore, when measuring a fitting with a caliper, it is impossible to &quot;convert&quot; the result to inches\u2014you must refer to a threaded connection table.<\/p>\n<h2> Comparison table of metric and inch threads.<\/h2>\n<table>\n<tbody>\n<thead>\n<tr>\n<th> Characteristic<\/th>\n<th> Metric thread<\/th>\n<th> Inch thread<\/th>\n<\/tr>\n<\/thead>\n<\/tbody>\n<tbody>\n<tr>\n<td> Unit<\/td>\n<td> Millimeter<\/td>\n<td> inch (25.4 mm)<\/td>\n<\/tr>\n<tr>\n<td> Jump description<\/td>\n<td> Distance between turns in mm (e.g. 1.5)<\/td>\n<td> Number of threads per inch (e.g. 20 TPI)<\/td>\n<\/tr>\n<tr>\n<td> Contour angle<\/td>\n<td> 60\u00b0<\/td>\n<td> 60\u00b0 (UNC, UNF, NPT) or 55\u00b0 (BSW, G, R)<\/td>\n<\/tr>\n<tr>\n<td> Approximate markings<\/td>\n<td> M8, M10\u00d71.25<\/td>\n<td> 1\/4\u2033-20 UNC, G 1\/2, 1\/2\u2033 NPT<\/td>\n<\/tr>\n<tr>\n<td> Standards<\/td>\n<td> ISO (in Poland PN-ISO)<\/td>\n<td> ANSI\/ASME (USA), BS, ISO 228 and ISO 7 (pipes)<\/td>\n<\/tr>\n<tr>\n<td> Where will you meet?<\/td>\n<td> Most of the screws, machines, cars and equipment in Europe and Asia<\/td>\n<td> American equipment, old British machines, hydraulics, camera tripods.<\/td>\n<\/tr>\n<tr>\n<td> Interchangeability<\/td>\n<td colspan=\"2\"> Usually no - even with a similar diameter, the pitch and angle are different.<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<h2> Where can I find inch threads in Poland?<\/h2>\n<p> In everyday life, we almost always encounter metric threads. Imperial threads are found primarily in a few places:<\/p>\n<ul>\n<li> <strong>Plumbing, gas and heating systems<\/strong> \u2013 connectors, valves, taps and hoses have G or R threads, for example, 1\/2\u2033, 3\/4\u2033, 1\u2033;<\/li>\n<li> <strong>Equipment from the USA<\/strong> \u2013 cars, motorcycles, automobiles and electronics designed in the inch system;<\/li>\n<li> <strong>Photography<\/strong> \u2013 the camera is attached to the tripod using a 1\/4\u2033-20 thread;<\/li>\n<li> <strong>Old British machine tools<\/strong> - with Whitworth thread.<\/li>\n<\/ul>\n<h2> How to determine whether a thread is metric or inch?<\/h2>\n<ul>\n<li> <strong>Measure the outside diameter<\/strong> Vernier calipers. Readings near millimeters (6, 8, 10, 12 mm) indicate metric threads; values such as 6.35 mm (1\/4 inch) or 9.5 mm (3\/8 inch) indicate inch threads.<\/li>\n<li> <strong>Check the thread pitch with a thread gauge<\/strong> . It has separate metric (mm) and inch (TPI) blades. The blade that fits flush indicates the thread type.<\/li>\n<li> <strong>In plumbing<\/strong> Compare the result with the pipe thread table: a diameter of approximately 21 mm usually corresponds to G 1\/2, approximately 26.4 mm \u2013 G 3\/4.<\/li>\n<li> <strong>Don&#039;t apply excessive force.<\/strong> A bolt that only tightens two or three turns and then stops likely has a different thread. Tightening it with a wrench will damage both components.<\/li>\n<li> <strong>When working with gas and pressure equipment<\/strong> Use the manufacturer&#039;s documentation and entrust the work to an authorized installer.<\/li>\n<\/ul>\n<h2> Frequently Asked Questions (FAQ)<\/h2>\n<p> <strong>Can you screw an inch screw into a metric thread?<\/strong><\/p>\n<p> Generally speaking, no. Even with similar diameters, the thread pitch and often the thread angle vary. A screw may engage several threads, but tightening it too much will damage the threads, and the connection will not last.<\/p>\n<p> <strong>What does M10\u00d71.25 mean?<\/strong><\/p>\n<p> This is a metric thread with a nominal diameter of 10 mm and a fine pitch of 1.25 mm. The designation M10 itself denotes the same thread with a normal pitch of 1.5 mm.<\/p>\n<p> <strong>Why is the thread diameter of 1\/2 inch approximately 21 mm?<\/strong><\/p>\n<p> Because in pipe threads, 1\/2&quot; is the nominal pipe size, not the thread diameter. A G 1\/2&quot; thread according to ISO 228 has an outside diameter of 20.955 mm.<\/p>\n<p> <strong>What is the difference between G and R threads?<\/strong><\/p>\n<p> Both threads are Whitworth-type and have a 55\u00b0 thread angle. The G thread (ISO 228) is cylindrical and does not provide a thread seal\u2014a gasket or O-ring seal is used. The R thread (ISO 7) is conical and provides a thread seal, typically with tape or paste.<\/p>\n<p> <strong>What is the angle of a metric thread and what is the angle of an inch thread?<\/strong><\/p>\n<p> In the ISO metric system, the angle is 60\u00b0. In the US imperial system (UNC, UNF, NPT), the angle is also 60\u00b0, and in the British Whitworth system, including G and R tubulars, the angle is 55\u00b0.<\/p>\n<h2> See also<\/h2>\n<ul>\n<li> What is the difference between alternating current and direct current?<\/li>\n<li> What is the difference between 95 and 98 octane gasoline?<\/li>\n<li> What is the difference between LR20 and R20 batteries?<\/li>\n<li> What is the difference between in-ear headphones and earbuds?<\/li>\n<\/ul>","protected":false},"excerpt":{"rendered":"<p>Metric threads differ from inch threads in their units of measurement and description: in metric threads, the diameter and pitch are indicated in millimeters (for example,<\/p>","protected":false},"author":1,"featured_media":176250,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[67,20],"tags":[70],"class_list":["post-176249","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-vopros-otvet","category-fakty","tag-chem-otlichaetsya"],"_links":{"self":[{"href":"https:\/\/bukvaved.top\/en\/wp-json\/wp\/v2\/posts\/176249","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/bukvaved.top\/en\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/bukvaved.top\/en\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/bukvaved.top\/en\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/bukvaved.top\/en\/wp-json\/wp\/v2\/comments?post=176249"}],"version-history":[{"count":1,"href":"https:\/\/bukvaved.top\/en\/wp-json\/wp\/v2\/posts\/176249\/revisions"}],"predecessor-version":[{"id":176251,"href":"https:\/\/bukvaved.top\/en\/wp-json\/wp\/v2\/posts\/176249\/revisions\/176251"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/bukvaved.top\/en\/wp-json\/wp\/v2\/media\/176250"}],"wp:attachment":[{"href":"https:\/\/bukvaved.top\/en\/wp-json\/wp\/v2\/media?parent=176249"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/bukvaved.top\/en\/wp-json\/wp\/v2\/categories?post=176249"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/bukvaved.top\/en\/wp-json\/wp\/v2\/tags?post=176249"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}