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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).
For buttress threads, the triangle is scalene. The theoretical triangle is usually truncated to varying degrees (that is, the tip of the triangle is cut short). A V-thread in which there is no truncation (or a minuscule amount considered negligible) is called a sharp V-thread. Truncation occurs (and is codified in standards) for practical ...
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
A screw thread, often shortened to thread, is a helical structure used to convert between rotational and linear movement or force. A screw thread is an inclined plane wrapped around a cylinder or cone in the form of a helix, with the former being called a straight thread and the latter called a tapered thread.
[2] [3] It is one of the strongest symmetric thread profiles; however, for loads in only one direction, such as vises, the asymmetric buttress thread profile can bear greater loads. 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]
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Thread run-outs and thread undercuts for ISO metric threads in accordance with DIN 13-1: Active: DIN 76-2: Thread run-outs and thread undercuts for pipe threads conforming to ISO 228 part 1: Active: DIN 76-3: Runouts, Undercuts for Trapezoidal Threads, Buttress Threads and Knuckle Threads and other Threads of Coarse Pitch: Active: DIN 78 ...