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The major minus pitch technique also works for inch-based threads, but you must first calculate the pitch by converting the fraction of threads-per-inch (TPI) into a decimal. For example, a screw with a pitch of 1/20 in (20 threads per inch) has a pitch of 0.050 in and a 1 ⁄ 13 in pitch (13 threads per inch) has a pitch of 0.077 in.
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).
While the above is a common use of center drill bits, it is a technically incorrect practice and should not be considered for production use. The correct tool to start a traditionally drilled hole (a hole drilled by a high-speed steel (HSS) twist drill bit) is a spotting drill bit (or a spot drill bit, as they are referenced in the U.S.). The ...
Text on current page, section 6 is: Jobber-length drill Jobber-length drills are the most common type of drill. The length of the flutes is between nine and fourteen times the diameter of the drill, depending on the drill size.
Every other chart I've ever seen calls for a 3.3mm drill for M4x0.70 tap. This may be same as M6 example above, where entry in chart is actually a 60% thread, but it's claiming 75% and does not list the 75% thread drill bit size of 3.3mm.Bmeyette 17:26, 10 March 2014 (UTC)
The drill bit is not held solidly in the chuck, but can slide back and forth like a piston; it does not slip during rotation due to the non-circular shank cross-section, matching the chuck. The hammer of the drill acts to accelerate only the drill bit itself, and not the large mass of the chuck, which makes hammer drilling with an SDS shank ...