A good tap drill is 85% (± 2 pp) of major diameter for coarse threads, and 90% (± 2 pp) of major diameter for fine threads. [1] a b c d e "Continuous Drill Bit Sizes". Archived from the original on 19 July 2006 . Retrieved 29 August 2006.

Regarding the proportion of tap drill to thread major diameter, for standard V threads ( ISO V thread and UTS V thread), there are several rules of thumb with strong predictive power: The drill sizes that are near this are 9.3mm (0.366 in) and letter U (0.368 in). In addition, 9.5mm (0.374 in), and 3⁄ 8 in (0.375 in) will work well, although major minus pitch by itself does not tell you this; but the 85% ± 2 pp guideline supports it. Fit the die with the sizing information on the die facing up and the top screw fitting into the slot, making sure all the screws are loose to allow the die to sit flush. Example (metric, coarse): For M7.0×1.0 (an intended screw with a diameter of 7.0mm and a pitch of 1mm between each thread, which is considered coarse), 7.0 mm × 0.85 = 5.95 mm.a b c d e "Tap Drill Sizes and Calculator". newmantools.com . Retrieved 4 August 2006. {{ cite web}}: External link in |work= ( help) Standard metric drill sizes used for metric taps of the size indicated in the tap size column. Drill bit diameter 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. Your result will only land near a tap drill size (not directly on one).

Smaller than M4 you readily risk breaking taps in your workpiece (taps are harder than drill bits, so this might mean you've ruined your workpiece). When it comes to tapping holes, the size of the drill bit is important. If the hole is too small, the tap will break. If the hole is too large, the fit will be sloppy and the threading will be weak. For a 10 mm tap, the ideal drill bit size is 11/32″. This will create a tight fit that is strong and durable. However, it is also important to use a sharp drill bit.As per the ISO metric screw thread standard, the thread depth should be 0.614 x pitch, which is why a smaller pitch number also results in a lower thread depth value. Now engineers can sit down and manually calculate the right tap drill. Or they can consult a tap drill chart like those found in the next section. The tap drill size for the M10 1.5 pitch is 8.5 mm. This is the size of the hole that will be created when using a tap with this drilling speed. It is important to note that this number will change depending on the specific tool being used and the type of metal being drilled. For example, stainless steel [ 1] will require a different size tap drill than carbon steel. Conclusion The drill sizes that are near this are letter U (0.368 in; 84.2%), 9.5mm (0.374 in; 85.6%), and 3⁄ 8 in (0.375 in; 85.8%); any of these will work well. a b c d e "Tap Drill Sizes for Universal and M-Profile Screw Threads". precisiontwistdrill.com . Retrieved 4 August 2006. {{ cite web}}: External link in |work= ( help) The M10 tap drill size is a standard used for machining threads. It is defined as the major diameter of the thread in millimeters minus the pitch of the thread. The M10 tap drill size is used for both metric and imperial units of measurement. The taps used to create the threads are also marked with the M10 designation. The M10 tap drill size is generally used for holes that are 10 mm in diameter.

Once through the material using this tap repeat the process using the tap with 2 grooves and then finally again using the tap with no grooves. a b c d e "Tap & Clearance Drills For Common Screws". Small Parts Inc. Retrieved 7 October 2010. {{ cite web}}: External link in |work= ( help) [ dead link] The drill sizes that are near this are 6.3mm (90%), 1⁄ 4 in (90.7%), 6.4mm (91.4%), and 6.5mm (92.9%); any of these will work well.Keep turning until the depth of thread is achieved, there should be no resistance once the cut has been made level and squre to the rod Theoretical percentage of thread should not be relied upon for threads of included angles other than 60 degrees.