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Number drill bit gauge sizes range from size 80 (the smallest) to size 1 (the largest) followed by letter gauge size A (the smallest) to size Z (the largest). Although the ASME B94.11M twist drill standard, for example, lists sizes as small as size 97, sizes smaller than 80 are rarely encountered in practice.
For both of these rules of thumb (85%/90% and major minus pitch), the tap drill size yielded is not necessarily the only possible one, but it is a good one for general use. The 85% and 90% rules works best in the range of 1 ⁄ 4 –1 in (6.4–25.4 mm), the sizes most important on many shop floors. Some sizes outside that range have different ...
In Japan, the male sizes are often designated as DTC-20, DTC-27, DTC-40 (discontinued) and DTC-45 corresponding to a respective screw head size of 3.2 mm, 4.6 mm, 6.4 mm and 7.7 mm; with the size of the screw measured across the widest portion of the mating part of the head. The most common sizes in use for consumer electronics are DTC-20 and ...
A pilot hole may be drilled the full extent of the final hole, or may only be a portion of the final depth. The pilot drill may be a standard twist drill, another type of drill bit appropriate for the material, or, when the primary purpose is precisely locating a hole, may be made with a short, stiff center drill.
Masonry bits typically are used with a hammer drill, which hammers the bit into the material being drilled as it rotates; the hammering breaks up the masonry at the drill bit tip, and the rotating flutes carry away the dust. Rotating the bit also brings the cutting edges onto a fresh portion of the hole bottom with every hammer blow.
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.