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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.
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. More screw threads are produced each year than any other machine element. [1] Threads are generally produced according to one of the many standards of thread systems.
The term fine adjustment screw typically refers to screws with threads from 40–100 TPI (Threads Per Inch) (0.5 mm to 0.2 mm pitch) and ultra fine adjustment screw has been used to refer to 100–254 TPI (0.2 mm to 0.1 mm pitch). These screws are most frequently used in applications where the screw is used to control fine motion of an object.
The thread pitch increases with diameter in steps specified on a chart. The Whitworth thread system was later to be adopted as a British Standard to become British Standard Whitworth (BSW). An example of the use of the Whitworth thread are the Royal Navy's Crimean War gunboats.
Coarse threads install much faster as they require fewer turns per unit length. Finer threads are stronger as they have a larger stress area for the same diameter thread. Fine threads are less likely to vibrate loose as they have a smaller helix angle and allow finer adjustment. Finer threads develop greater preload with less tightening torque. [5]
United States Standard thread (USS thread), also known as Sellers Standard thread, [1] Franklin Institute thread [1] and American Standard thread, [2] is a standard for inch based threaded fasteners and washers. [3] The USS standard is no longer supported. It, together with the SAE fastener standard, was incorporated into the Unified Thread ...
Knuckle threads with a flat 30 degree flank thread angle are standardized in DIN 405 for inch pitches and diameters ranging from 8 mm to 200 mm. [3] A more recent standard DIN 20400 uses metric thread pitch and lists diameters from 10 mm to 300 mm. [4] As DIN is a German organization, many instances of the DIN thread charts [5] write numbers with a comma as the decimal marker.
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".