Pilot Hole depth is very important factor. They not only make it easier to drive the screw, but also prevent the screw from getting stripped or the drill bit from breaking. Drill bits come in various sizes to accommodate different screw sizes.įor harder materials like metal, pilot holes are particularly important. The drill bit should be of the same diameter as the screw’s inner core (not including the threads). You should use a pilot hole drill bit to drill a pilot hole. This ensures that the screw threads can bite into the material and hold the screw firmly in place. Generally, the pilot hole should be smaller than the diameter of the screw. The size of the pilot hole is determined by the size of the screw. It also makes it easier to drive the screw straight into the material. The main purpose of a pilot hole is to guide the screw and prevent the material from splitting or cracking due to the pressure exerted by the screw. How to Drill Pilot Hole Without a Drill Bit?Ī pilot hole is a small hole drilled into a material, such as wood or metal, before driving a screw into it.How to Drill a Pilot Hole in Wood and Metal?.What are the Recommended Drill Bit Sizes for Softwood and Hardwood Pilot Holes?.Join 100,000+ CNC'ers! Get our latest blog posts delivered straight to your email inbox once a week for free. Matter of fact, you get a BUNCH of free calculators! Like what you read on CNCCookbook? Here’s the best news: you get the Drill Bit Size Calculator free for life when you sign up for the 30-day free trial of our G-Wizard Machinists Calculator. Plus, the box at top lets you quickly search to sizes near that one. With the checkboxes at the top, you can limit what you’re seeing to exactly what you want. That’s why I built a Drill Size Chart into my G-Wizard software: I prefer software because it can search, copy values to where they’re needed, and generally save you effort. The thing about charts, especially wall charts, is they’re convenient for some things, but unwieldy for others. Check out our article on tap drill sizes to find a much better way. Don’t just pick the first tap drill size you come across, not even the one in our Drill Chart below. While it may seem logical that most holes are nice round numbers in size, certain operations benefit from a lot of intermediate sizes. Number and Letter Sizes are in common use in the US, and to a lesser extent the UK (rapidly moving to metric), but are no longer in use for most of the rest of the world which has gone fully metric. Letter Sizes are Imperial drill bit sizes designated A (smallest) to Z (largest). The numbered sizes are based on but unfortunately are not identical to the Stubs Steel Wire Gauge, which originated in 19th century Great Britain. In practice, you will seldom see number sizes past #80. The ASME B94.11M twist drill standard establishes number drill bit sizes from size 1 to 97. Number Drill Bit Sizes & Letter Drill Bit Sizes Decimal Equivalence ChartĪ good drill size chart can also be used as a handy decimal equivalence chart as well as to convert decimal sizes to metric. After that they run in 1/32″ increments up to 2 1/4″, then in 1/16″ increments to 3″, 1/8″ increments to 3 1/4 inches, then there’s a 3 1/2″ size. Fractional-Inch Drill Bit Sizesįractional-inch sizes are in common use in the US and generally run from 1/64 inch up to 1 3/4 inch in 1/64″ increments. There are also Reynard Series of preferred metric drill sizes. So for N = 2, it’s 2 – 0.1, etc.įrom 1 through 2.95mm, using N from 10 through 29, we get:įor 3 through 13.9mm, with N from 30 to 139:įor 14 through 25mm, and N from 14 through 25: Standard metric lengths (from standards like BS 32*) define metric drill bit sizes using this system:įor 0.2 to 0.98mm, sizes use N from 2 through 9: It covers decimal, fractions, numbered drill bits, letter drill sizes, metric drill bits, and probably a few more things I forgot to mention.įor more on twist drills in general, see our twist drill article for all the different types and tips for holemaking with them. It’s very convenient to have a drill chart around with bit sizes, so we thought we’d put one here for you.
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