There are not many options that are slightly larger than 8.50mm or R. What if I want to drill a hole for a tap to cut M10 threads with 70% engagement? Okay – so 75% engagement for M10 would mean an 8.50mm or R (~8.61mm) drill bit size, and 50% engagement for M10 would mean 9.00mm or T (~9.09mm). (When looking at reference charts online, it’s a good idea to double check with other references.) This is according to the Little Machine Shop chart, or others’. If I wanted to tap ferrous materials such as steel, 50% thread engagement would mean a 9.00mm drill bit size, or T as the closest imperial letter gauge drill bit size, which is 0.358″. I have a letter drill bit set, but if not I’d have to buy either size. There’s no fractional equivalent close enough. (I have also seen at least one chart list Q as the closes imperial drill bit size.) The closest imperial drill bit size is R, which is 0.339″ or ~8.61mm. To prep a through-hole for an M10 x 1.5 tap, that chart says I’ll need an 8.50 mm drill size for 75% thread engagement in non-ferrous materials. This size drill bit should be used for drilling the initial hole that will then be tapped.Here’s a Little Machine Shop chart for metric and inch tap and clearance drill sizes. Lastly, the recommended tap drill size is provided for each standard tap size. The drill size chart contains tools up to 1.5 inches in diameter, but larger tools are also commonly used.įor each thread count, the equivalent thread pitch is provided and for metric taps, the approximate thread count is shown based on the pitch. The metric system uses the thread pitch, which is the distance between threads, measured in millimeters. In the fractional and screw size systems, the thread count is used, measured in threads per inch, such as UNF threads and UNC threads. The thread spacing can be coarse or fine, will be listed after the diameter. A screw size number corresponds to a diameter which is larger for a higher screw size. Fractional sizes are listed in inches, metric sizes are listed in millimeters following the letter "M". The tap size chart is a table that lists standard size taps, specifying the diameter and thread spacing, for fractional, metric, and screw sizes. The decimal equivalents of the diameters are shown in both English and Metric units. The wire gauge and letter systems refer to tool diameters that increase as the wire gauge decreases from #107 to #1 and then continues from A to Z. Fractional sizes are measured in inches, while metric sizes are measured in millimeters. The drill size chart is a table list standard size drill bits in several measurement systems, including fractional, metric, wire gauge number, and letter. People would need a drill size chart and tap size chart to determine the proper tap drill for a certain thread size or proper tap for an existing hole. One of the most common ways to produce the thread holes is to drill a hole of the right size with a drill bit and tap it with a tap. When manufacturing custom CNC machining parts, holes with screw threads are often required for fastening the finished part or facilitating the building. What is the Drill and Tap Size Chart and Why to Use Them? When it comes to the selection of drill bit sizes and tap sizes, there are standard drill and tap size chart for reference. Drilling is a process of producing a hole while tapping is a technique used to cut a thread inside a hole, so the drill bit and tapping tool are often used in sequential to fabricate CNC parts with thread holes.
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