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This is known as a right-handed (RH) thread, because it follows the right-hand grip rule. Threads oriented in the opposite direction are known as left-handed (LH). By common convention, right-handedness is the default handedness for screw threads. Therefore, most threaded parts and fasteners have right-handed threads.
Most screws are tightened by clockwise rotation, which is called a right-hand thread. [4] [5] Screws with a left-hand thread are used in exceptional cases, such as where the screw will be subject to counterclockwise torque, which would tend to loosen a right-hand screw. For this reason, the left-side pedal of a bicycle has a left-hand thread. [6]
It normally consists of two threaded eye bolts, one screwed into each end of a small metal frame, one with a conventional right-hand thread and the other with a left-hand thread. The tension can be adjusted by rotating the frame, which causes both eye bolts to be screwed in or out simultaneously, without twisting the eye bolts or attached cables.
The shank length is not always the same at the thread length, which is the case if the insert has a threadless portion (sub-shank) Tenon designates the thread length; Shoulder designates the barrel diameter in front of the thread portion; Unless otherwise mentioned, right hand threads are assumed. Left hand threads are designated "LH".
The Unified Thread Standard (UTS) defines a standard thread form and series—along with allowances, tolerances, and designations—for screw threads commonly used in the United States and Canada. It is the main standard for bolts, nuts, and a wide variety of other threaded fasteners used in these countries.
Left-handed screw threads are also used in some other applications: Where the rotation of a shaft would cause a conventional right-handed nut to loosen rather than to tighten due to fretting induced precession. Examples include: The left hand pedal on a bicycle. [21] [23] The left-hand screw holding a circular saw blade or a bench grinder wheel on.
Similarly, one may construct a double-thread screw provided that the helix angle of the two cuts is the same, and that the second cut is positioned in the uncut material between the grooves of the first. For certain applications, triple and quadruple threads are in use. [3] The helix may be cut either right hand or left hand.
the thread size; Threads are normally right-hand. For left-hand threads, the letters, LH, are appended. Example: Pipe thread EN 10226 Rp 2 + 1 ⁄ 2. The terminology for the use of G and R originated from Germany (G for gas, as it was originally designed for use on gas pipes; R for rohr, meaning pipe.)