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Standardization efforts in the late 19th and the early part of the 20th century reduced the range of sizes considerably. Now, it is less common to see machine screws larger than #14, or odd number sizes other than #1, #3 and #5. Even though #14 and #16 screws are still available, they are not as common as sizes #0 through #12. [citation needed]
My machinists and my fastener suppliers have told me that 1-12UNF is an old standard, and 1-14UNF is the new standard for 1" fine thread. I don't have access to the ANSI documents, so I can't reference those, however, these sites do reflect the change: [4] , [5] , [6] Khawki02 ( talk ) 19:32, 15 December 2009 (UTC) [ reply ]
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.)
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 Unified thread angle is 60° and has flattened crests (Whitworth crests are rounded). From 1 ⁄ 4 in up to 1 + 1 ⁄ 2 in, thread pitch is the same in both systems except that the thread pitch for the 1 ⁄ 2 in bolt is 12 threads per inch (tpi) in BSW versus 13 tpi in the UNC.
A diagram of an ISO metric or Unified thread, showing dimensions relative to the pitch (P) and thread height (H). Due to different standards, ISO and UTS share the same geometry, but not absolute dimensions. Also shown is the location rounding permissible in internal (dark grey, top) and external (light grey, bottom) threads. Key. P: Pitch; H ...
Example (inch, coarse): For size 7 ⁄ 16 (this is the diameter of the intended screw in fraction form)-14 (this is the number of threads per inch; 14 is considered coarse), 0.437 in × 0.85 = 0.371 in. Therefore, a size 7 ⁄ 16 screw (7 ⁄ 16 ≈ 0.437) with 14 threads per inch (coarse) needs a tap drill with a diameter of about 0.371 inches.
For example, 1 ⁄ 2-13 belongs to the UNC series (Unified National Coarse) and 1 ⁄ 2-20 belongs to the UNF series (Unified National Fine). Similarly, M10 (10 mm nominal outer diameter) as per ISO 261 has a coarse thread version at 1.5 mm pitch and a fine thread version at 1.25 mm pitch.