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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.
One aspect of this method of sizing is that the size increment between drill bits becomes larger as bit sizes get smaller: 100% for the step from 1/64 to 1/32, but a much smaller percentage between 1 47/64 and 1 3/4. 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.
The brad point drill bit (also known as lip and spur drill bit, and dowel drill bit) is a variation of the twist drill bit which is optimized for drilling in wood. Conventional twist drill bits tend to wander when presented to a flat workpiece. For metalwork, this is countered by drilling a pilot hole with a spotting drill bit.
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. So a 1⁄2 in (12.7 mm) diameter drill will be able to drill a hole 4 1⁄2 in (114.3 mm) deep since it is nine times the diameter in length. A 1⁄8 in (3.2 mm) diameter ...
the thread size; Threads are normally right-hand. For left-hand threads, the letters, LH, are appended. Example: Pipe thread EN 10226 Rp 2 + 1 ⁄ 2. The terminology for the use of G and R originated from Germany (G for gas, as it was originally designed for use on gas pipes; R for rohr, meaning pipe.)
Many screws used in electrical applications (for example, a typical NEMA 5-15R, breaker screws, and conduit screws) use a combination of a slotted/Phillips/Robertson screw head. A few tool manufacturers make bits to engage this screw head better than the traditional Phillips allowing for more torque before camout, for example, the C1 and C2 ...
In deciding which drill(s) to use it is important to consider the task at hand and evaluate which drill would best accomplish the task. There are a variety of drill styles that each serve a different purpose. The subland drill is capable of drilling more than one diameter. The spade drill is used to drill larger hole sizes.
Confusion can arise because each Whitworth hexagon was originally one size larger than that of the corresponding BSF fastener. This leads to instances where for example, a spanner marked 7 ⁄ 16 BSF is the same size as one marked 3 ⁄ 8 W. In both cases the spanner jaw width of 0.710 in, the width across the hexagon flat, is the same.