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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.
The diameters are sometimes given approximately in fractions of an inch (e.g. the major diameter of a #6 screw is 0.1380 in, approximately 9 ⁄ 64 in = 0.140625 in. The pitch P is the distance between thread peaks.
Drill bit sizes are written as irreducible fractions. So, instead of 78/64 inch, or 1 14/64 inch, the size is noted as 1 7/32 inch. Below is a chart providing the decimal-fraction equivalents that are most relevant to fractional-inch drill bit sizes (that is, 0 to 1 by 64ths).
A Robertson screw, ... Screwdriver bits in different sizes for Robertson screws. ... Screw sizes Fraction Range in mm Orange #00 #1, #2: 0.05
British Standard Whitworth (BSW) is an imperial-unit-based screw thread standard, devised and specified by Joseph Whitworth in 1841 and later adopted as a British Standard. It was the world's first national screw thread standard, and is the basis for many other standards, such as BSF, BSP, BSCon, and BSCopper.
BS 93:1951 — Specification for British Association (B.A.) screw threads with tolerances for sizes 0 B.A. to 16 B.A. BS 93:2008 — British Association (B.A.) screw threads — Requirements The angle of the thread is 47.5° [ 4 ] : 2 and the depth of thread is 0.6 times the pitch with rounded tops and bottoms.
Similar to a wood screw, except that it is generally much larger running to lengths up to 15 in (381 mm) with diameters from 0.25–0.5 in (6.35–12.70 mm) in commonly available (hardware store) sizes (not counting larger mining and civil engineering lags and lag bolts) and it generally has a hexagonal drive head.
William Sellers originally developed the USS thread, and set forth many of its details in his paper, "A System of Screw Threads and Nuts", presented in April 1864 to the Franklin Institute. In 1898, the standard for metric threaded fasteners was established.