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The major minus pitch technique also works for inch-based threads, but you must first calculate the pitch by converting the fraction of threads-per-inch (TPI) into a decimal. For example, a screw with a pitch of 1/20 in (20 threads per inch) has a pitch of 0.050 in and a 1 ⁄ 13 in pitch (13 threads per inch) has a pitch of 0.077 in.
A 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 a dash or sometimes the multiplication sign, × (e.g. M8-1.25 or M8×1.25). If the pitch is the normally used "coarse" pitch listed in ISO 261 or ...
Pitch and TPI describe the same underlying physical property—merely in different terms. When the inch is used as the unit of measurement for pitch, TPI is the reciprocal of pitch and vice versa. For example, a 1 ⁄ 4-20 thread has 20 TPI, which means that its pitch is 1 ⁄ 20 inch (0.050 in or 1.27 mm).
The pitch P is the distance between thread peaks. For UTS threads, which are single-start threads, it is equal to the lead, the axial distance that the screw advances during a 360° rotation. UTS threads do not usually use the pitch parameter; instead a parameter known as threads per inch (TPI) is used, which is the reciprocal of the pitch.
where is the tap drill size, is the major diameter of the tap (e.g., 10 mm for a M10×1.5 tap), and pitch is the pitch of the thread (1.5 mm in the case of a standard M10 tap) and so the correct drill size is 8.5 mm. This works for both fine and coarse pitches, and also produces an approximate 75% thread.
Mixing metric and imperial threads can result in finer differentials while still using standard threads, they can be calculated in the same way as a metric differential but the TPI of the imperial thread must be converted to a metric pitch measurement. For example a 26 TPI thread has a pitch of ~0.977 mm and when paired with a 1.0 mm pitch ...
Thread pitch P Hand-tight engagement [6] Effective thread [6] Overall length L 4 [6] Actual outside diameter D Tap drill; Length L 1 Turns Diameter E 1 Length L 2 Turns Diameter E 2; inch inch −1 inch mm inch inch inch inch inch inch mm inch mm 1 ⁄ 16: 27 0.03703704 0.9407 0.1600: 4.32: 0.28118 0.2611: 7.05: 0.2875 0.3896 0.313 7.950 1 ...
Metric trapezoidal threads [1] Tr 30° DIN 103 Buttress threads [6] S 45° DIN 2781 German buttress threads [6] S 30° DIN 513 Square threads [1] Sq 0° (parallel) ? Panzergewinde, "steel conduit thread" Pg 80° DIN 40430 British Association (BA) thread: BA 47° 30' = 47.5° BS 93:2008 Löwenherz thread [8] 53° 8' ≈ 53.1° Bodmer thread [9] 50°