6Pcs Drill Tap Bits,M3 M4 M5 M6 M8 M10 Metric Thread HSS Drill and Tap Bits 1/4" Hex Shank Thread Screw Tap Tool Set

Product Information

The “M” indicates the “metric diameter” of its thread (see tap drill chart below), which in our case is 4 mm. The second number (0.7) is the pitch which corresponds to the distance between two adjacent threads in millimeters. Finally, 20 is the length of the bolt in mm, measured from the tip of the thread to the bottom of the head (with the exception of oval headed bolts). a b c d e "Decimal Equivalents". Ohio State University. Archived from the original on 2 September 2006 . Retrieved 29 August 2006. {{ cite web}}: External link in |work= ( help) 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] 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. Tighten up the screw on the die holder to keep the die in place, ensure all the screws fit in the indences in the die.

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. 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.

General background and Pre-checks

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). 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. Example (inch, fine): For 7⁄ 16-20 (same diameter as the previous example, but this time with 20 threads per inch, which is considered fine), 0.437 in × 0.90 = 0.393 in (i.e., if the threads are to be fine, then a slightly larger diameter drill bit should be used before tapping the hole for the screw).

Example (metric fine): For M7.0×0.5, major minus pitch yields 6.5, which at 92.9% happens to be an example that pushes over the outer bound of the 90% ± 2 pp, but major minus pitch is still valid, although smaller drills (6.3mm, 1⁄ 4, 6.4mm) will work well. Based on the desired nominal size, look at the desired standard column to determine the minimum outside diameter of the component for the threads. 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. The drill sizes that are near this are 15⁄ 64 in (85%), 6.0mm (85.7%), and 6.1mm (87.1%); any of these will work well.The major minus pitch also works for inch-based threads, but you must first determine the pitch by looking at the number of treads per inch (TPI; for example, 1⁄ 20 = 0.050 and 1⁄ 13 ≈ 0.077), and your result will only land near a tap drill size (not directly on one). Keep turning until all the way through the material and most of the way through the thread, there should be no resistance once the cut has been made the full distance through the material when turning in or out using the tap wrench. 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. The result is 4.0 mm - 0.8444 mm = 3.1666 mm, which is the necessary diameter for the drilled hole. There are 'non-standard' M4 thread forms, which will have different pitches, which are incompatible with standard M4. For example M4x0.5mm. This would be referred to as "M4 fine", but some people would refer to any M4 pitch less than 0.70mm as M4 fine, so take care!