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Such an appropriately sized drill is called a tap drill for that size of thread, because it is a correct drill to be followed by the tap. Many thread sizes have several possible tap drills, because they yield threads of varying thread depth between 50% and 100%.
Pipe Thread Form ANSI B1.20.3-1976 (R2013) Dryseal Pipe Threads (Inch) Pipe Thread Form ASME B1.20.7-1991 (R2013) Hose Coupling Screw Threads - Inch: Pipe Thread Form ASME B1.21M-1997 (R2013) Metric Screw Threads - MJ Profile: V Thread Form BS 84: Tables of BS Whitworth, BS Fine and BS Pipe Threads: V Thread Form (55°) 1 ⁄ 4 ″-20 BSW ISO ...
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.
For example, for a 1/4-28 thread, any of these 3 tap drills may be acceptable: #3 (~75% thread), #2 (~60% thread), or 7/32 (~68% thread). In the case of M6-1.0, the rule of thumb that you mentioned, major minus pitch, yields a 5mm tap drill at ~75% thread. However, the tap drill that the chart mentions, 5.2mm, will give a ~60% thread, which is ...
For a taper thread, it is the diameter at the "gauge length" (plus/minus one thread pitch) from the small end of the thread. The taper is 1:16, meaning that for each 16 units of measurement increase in the distance from the end, the diameter increases by 1 unit of measurement.
The half-angle (between the taper surface and the axis of the pipe) is arctan(1 ⁄ 32) ≈ 1.7899° ≈ 1° 47′. The standard for Nominal Pipe Size (often abbreviated NPS, which should not be confused with the abbreviation NPS for the straight thread form standard) is loosely related to the inside diameter of Schedule 40 series of sizes.
The thread form is defined by flats at the tip and root of the thread form. This flat length is defined as the pitch divided by eight. The thread depth, which is from flat to flat is 0.6495 times the pitch. [4] For 1 ⁄ 4-inch (6.4 mm) screws and larger, the pitch is defined as: = +
where is the tap drill size, is the major diameter of the tap (e.g., 10 mm for a M10×1.5 tap), and pitch is the pitch of the thread (1.5 mm in the case of a standard M10 tap) and so the correct drill size is 8.5 mm. This works for both fine and coarse pitches, and also produces an approximate 75% thread.