{"id":2373,"date":"2012-05-16T14:53:26","date_gmt":"2012-05-16T18:53:26","guid":{"rendered":"http:\/\/labrigger.com\/blog\/?p=2373"},"modified":"2012-05-16T17:09:33","modified_gmt":"2012-05-16T21:09:33","slug":"notes_on_screws","status":"publish","type":"post","link":"http:\/\/labrigger.com\/blog\/2012\/05\/16\/notes_on_screws\/","title":{"rendered":"Miscellaneous notes on screws"},"content":{"rendered":"

\"\"<\/a><\/p>\n

Terms for metric and English screw size standards<\/h4>\n

These terms are all equivalent for most purposes:
\nmetric = ISO metric = ANSI mm
\nEnglish (US) = imperial (UK) = UTS = ANSI inch<\/p>\n

\"\"<\/p>\n

Major diameter<\/h4>\n

Metric screw sizes are easy to figure out.
\nM3: The “M” is for metric, and the “3” is the major (nominal) screw diameter in mm.<\/p>\n

English screw sizes are easy for large screw sizes.
\n1\/4-20: 1\/4 inch major diameter
\nFor smaller screw sizes, read the next section.<\/p>\n

The numbers for English screws<\/h4>\n

Two common sizes of small machine screws are #4-40 and #8-32. What do these numbers mean? As it says above, the second number refers to the thread pitch, and is reported as the threads per inch. However, the first numbers, the major (nominal) diameters, are a bit more complicated. Here’s how to convert them into inches:
\nmajor diameter in inches = 0.060 + (0.013 * N<\/em>)
\nWhere N<\/em> is the first number in the name of the screw.<\/p>\n

Thread pitch<\/h4>\n

To denote the thread pitch, the two main systems use different measures which are actually the inverse of each other<\/strong>. For metric screws, the pitch is measured in mm per thread<\/strong>. For example, M3 screws are typically 0.5 mm per thread. For English\/imperial screws, the thread pitch is measured in threads per inch<\/strong>. For example, 1\/4″-20 screws are 20 threads per inch.<\/p>\n

TLAs (Three Letter Abbreviations)<\/h4>\n

UNC, UNF, UNEF<\/strong>
\nThese are from the UTS<\/a> (Unified Thread Standard). It’s for English\/Imperial screw sizes. Each screw size (nominal diameter\/major diameter) is available in either a coarse (UNC), fine (UNF), or extra fine (UNEF) thread pitch; e.g., UNC = UNified thread standard Coarse.<\/p>\n

BSW, BSF, BSC<\/strong>
\nBSW<\/a> stands for British Standard Whitworth. Joseph Whitworth authored the first national screw standard in 1841, and it still carries his namesake. BSF is the variant with fine thread pitch. BSC is a variant used for Cycles (motorcycles and bicycles). UNC is based off of the BSW standard, but with a different shape to the threads. In some applications, UNC and BSW are interoperable. For example, the screw mount at the bottom of SLR cameras for tripod attachement is a BSW 1\/4-20 standard, but UNC 1\/4-20 screws can often be used in them.<\/p>\n

Fun fact for the day<\/h4>\n

One time in London, I needed a fine pitch tap and die set and the cheapest I could find was a BA set, so I bought that. The BA screw standard isn’t used much any more, but it’s an interesting standard.<\/p>\n

  • All of the screw sizes are defined in inches, but they come out to be nice round numbers in mm. For example, BA2 has a nominal diameter of 0.1260 inches, which is 3.200 mm.<\/li>\n
  • The standard is not a list of sizes, but rather one base size and then a formula to calculate all of the rest. Size BA0 is the base size, with a 0.2362 inch (6.00 mm) major diameter and 25.38 threads per inch (1 thread per mm). Wikipedia explains the formula for calculating the other sizes (link<\/a>).<\/li>\n

    (source<\/a>)
    \n(    via<\/a>)<\/p>\n","protected":false},"excerpt":{"rendered":"

    <\/a><\/p>\n

    Terms for metric and English screw size standards<\/p>\n

    These terms are all equivalent for most purposes:
    \nmetric = ISO metric = ANSI mm
    \nEnglish (US) = imperial (UK) = UTS = ANSI…<\/p>\n

    Read More<\/a><\/div><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[3],"tags":[],"class_list":["post-2373","post","type-post","status-publish","format-standard","hentry","category-tips"],"_links":{"self":[{"href":"http:\/\/labrigger.com\/blog\/wp-json\/wp\/v2\/posts\/2373","targetHints":{"allow":["GET"]}}],"collection":[{"href":"http:\/\/labrigger.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"http:\/\/labrigger.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"http:\/\/labrigger.com\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"http:\/\/labrigger.com\/blog\/wp-json\/wp\/v2\/comments?post=2373"}],"version-history":[{"count":10,"href":"http:\/\/labrigger.com\/blog\/wp-json\/wp\/v2\/posts\/2373\/revisions"}],"predecessor-version":[{"id":2395,"href":"http:\/\/labrigger.com\/blog\/wp-json\/wp\/v2\/posts\/2373\/revisions\/2395"}],"wp:attachment":[{"href":"http:\/\/labrigger.com\/blog\/wp-json\/wp\/v2\/media?parent=2373"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/labrigger.com\/blog\/wp-json\/wp\/v2\/categories?post=2373"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/labrigger.com\/blog\/wp-json\/wp\/v2\/tags?post=2373"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}