ISO 262 specifies a shorter list of thread dimensions – a subset of ISO 261. ISO 261 specifies a detailed list of preferred combinations of outer diameter D and pitch P for ISO metric screw threads. Internal threads are designated by upper case letters, G or H.

External threads are designated by lowercase letter, g or h. Tolerance classes defined in ISO 965-1 can be appended to these designations, if required (e.g. The length of a machine screw or bolt is indicated by a following × and the length expressed in millimetres (e.g. If the pitch is the normally used 'coarse' pitch listed in ISO 261 or ISO 262, it can be omitted (e.g. The relationship between the height H and the pitch P is found using the following equation where θ is half the included angle of the thread, in this case 30°: H = 1 2 tan ⁡ θ ⋅ P = 3 2 ⋅ P ≈ 0.866025 ⋅ P Designation Ī metric ISO screw thread is designated by the letter M followed by the value of the nominal diameter D (the maximum thread diameter) and the pitch P, both expressed in millimetres and separated by the multiplication sign, × (e.g. The outermost 1⁄ 8 and the innermost 1⁄ 4 of the height H of the V-shape are cut off from the profile. In the plane of the thread axis, the flanks of the V have an angle of 60° to each other. ISO metric threads consist of a symmetric V-shaped thread. Each thread is characterized by its major diameter, D ( D maj in the diagram), and its pitch, P. The design principles of ISO general-purpose metric screw threads ('M' series threads) are defined in international standard ISO 68-1. That is, an M6 screw has a nominal outer diameter of 6 millimetres and will therefore be a well-located, co-axial fit in a hole drilled to 6 mm diameter.īasic profile of all ISO metric screw threads, where the male part has the external thread on a bolt) will pass through easily to create a well-located connection to an internally threaded component (e.g. It indicates the diameter of smooth-walled hole that a male thread (e.g.

This is also referred to as the 'major' diameter in the information below. The 'M' designation for metric screws indicates the nominal outer diameter of the screw thread, in millimetres. They were one of the first international standards agreed when the International Organization for Standardization (ISO) was set up in 1947. The ISO metric screw thread is the most commonly used type of general-purpose screw thread worldwide. ( December 2020) ( Learn how and when to remove this template message)

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Metric bolts sizes m1.6