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The major diameter is given by 6p 1.2, [4]: 12 rounded to two significant figures in mm and the hex head size (across the flats) is 1.75 times the major diameter. BA sizes are specified by the following British Standards: BS 57:1951 — B.A. screws, bolts and nuts
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 standard designation for a UTS thread is a number indicating the nominal (major) diameter of the thread, followed by the pitch measured in threads per inch.For diameters smaller than 1 / 4 inch, the diameter is indicated by an integer number defined in the standard; for all other diameters, the inch figure is given.
Other (usually smaller) sizes may occur to reduce weight or cost, including the small series flange bolts defined in ISO 4162 which typically have hexagonal head sizes corresponding to the smaller 1st choice thread size (eg. M6 small series flange bolts have 8mm hexagonal heads, as would normally be found on M5 bolts). [10]
The contemporary square drive screw has all but replaced the Robertson screw proper and is commonly referred to as a Robertson because it has practically identical drive dimensions and the same colour identification system, but the contemporary square drive socket has parallel sides rather than tapered.
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.
ISO general purpose metric screw threads—Selected sizes for screws, bolts and nuts: V Thread Form ISO 724:1993: ISO general-purpose metric screw threads—Basic dimensions: V Thread Form ISO 725:2009: ISO inch screw threads—Basic dimensions: V Thread Form 51386 DIN 40400: Edison Thread: Round V Thread Form
To simplify matters, the term hexagon is used in this section to denote either bolt head or nut. Two spanners, both nominal size 5 ⁄ 8 in, with a diagram superimposed to show the logic that allows them both to be nominal size 5 ⁄ 8 in when their actual sizes are clearly different (across-flats distance vs screw diameter). The across-flats ...