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In oil field tubing, buttress thread is a pipe thread form designed to provide a tight hydraulic seal. The thread form is similar to that of Acme thread [10] but there are two distinct threaded portions of differing diameters and profiles, the larger having a wedging profile, with a tapered sealing portion in between the larger and smaller diameters.
This is most easily described for a square or buttress thread as the thread angle is 0 and has no bearing on the calculations. The unwrapped thread forms a right angle triangle where the base is π d m {\displaystyle \pi d_{\text{m}}} long and the height is the lead (pictured to the right).
Acme thread [6] 29° ASME/ANSI B1.5-1988 [7] 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 ...
The thread angle also has an effect on the strength of the threads; threads with a large angle have a wide root compared with their size and are stronger. Standard types of screw threads: (a) V, (b) American National, (c) British Standard, (d) Square, (e) Acme, (f) Buttress, (g) Knuckle
Buttress thread; Royal Microscopical Society (RMS) thread, also known as society thread, is a special 0.8-inch diameter × 36 thread-per-inch (TPI) Whitworth thread form used for microscope objective lenses. Microphone stands: 5 ⁄ 8-inch 27 threads per inch (TPI) Unified Special thread (UNS, USA and the rest of the world)
Acme Screw Threads: Trapezoidal Thread Form: Tr 60×9 ANSI/ASME B1.9-1973 (R2017) Buttress Inch Screw Threads: Breech-Lock Thread Form: ASME B1.10M-2004 (R2014) Unified Miniature Screw Threads: V Thread Form: 0.60 UNM ANSI/ASME B1.11-1958 (R2016) Microscope Objective Thread: V Thread Form ASME B1.13M-2005 (R2015) Metric Screw Threads: M Profile ...
The trapezoidal metric thread form is similar to the Acme thread form, except the thread angle is 30°. [4] [5] [6] It is codified by DIN 103. [7] While metric screw threads are more prevalent worldwide than imperial threads for triangular thread forms, the imperially sized Acme threads predominate in the trapezoidal thread form.
All that is required is to look closely at the thread form (I suggest starting with the Simple Buttress form) and do the maths. In the thread form shown 2 x f = 33% of the pitch, leaving the thread base at 66% of pitch. In a square thread form the thread base is never greater than 50% pitch.