This cookie is set by GDPR Cookie Consent plugin. These cookies ensure basic functionalities and security features of the website, anonymously. Necessary cookies are absolutely essential for the website to function properly. You’ll always want to know the intended depth of the hole and the screw thread information for the fastener. Once you understand what’s being expressed, things become a bit clearer. Your average tap drill chart might appear confusing at first. Some charts will also include a standard size of thread depth, depending on the application. Once that hole is created, it can be tapped with the right thread count or pitch. The more threads, the higher the minor diameter.Ī good tap drill chart will also suggest the correct bit size for the initial drilled hole. Major diameters refer roughly to the height of the thread itself, while minor diameters calculate the overall number of threads. You may also see charts that refer to major diameters and minor diameters. Metric measurements use thread pitch – the distance between threads, expressed in millimeters. The English system expresses a thread count – the number of screw threads per inch, also known as TPI. Screw thread sizes are expressed differently depending on the sizing system used. Machinists also use them to calculate the correct threading. Thread countĪ good tap drill chart doesn’t just give the diameter of the drill bit. Size 80 is the smallest, size 1 the largest.įractional – For standard English measurements (inches), drill bit diameters are expressed as a fraction of an inch – say, 1/16 inches.ĭecimal – Decimal sizing is used to express fractional equivalents in the metric system, given out to four places. Number – Twist bits (a particular kind of drill bit) are the most likely to use the letter and number systems. Letter – A-Z, with A being the smallest and Z the largest. ![]() Metric – The diameter of the bit given in standard metric sizes, typically expressed in millimeters. All of these systems refer to the diameter of the drill bit. Any given drill size chart might use several of the sizes at once. ![]() There are at least five common sizing systems in use. In fact, that’s where tap drill charts come in – they help machinists navigate the different terms and find the right size. But how to tell the correct size? You’ll find a number of different sizing systems in common use for measuring drill bits. Pre-drill a hole with the correct tap drill size, and you’ll ensure that all of your screws and threaded bolts will have a tight, close fit. You’ll also ruin the threads on both the fastener and in the threaded hole.ĭrilling the correct hole size and tapping the right thread pitch is essential for fasteners that stay tight and keep parts performing as required. Thread it incorrectly, and you’ll find that inserting the fastener is a much harder job than anticipated. Whether it’s a coarse thread or fine thread, matching the correct thread to your intended fastener is key to a good fit. Too small, and you won’t be able to make a connection at all – you’ll have to re-drill the hole. Drill a hole too large, and your screw, bolt, or pipe thread will be too loose. There are two basic steps to the process – drilling the hole with the correct drill bit size and then threading or “tapping” the hole.Įach step requires precise measurements. Drilling and tappingĬreating a threaded hole is one of the most common machine shop tasks. That’s what we’re here to do – give you a tap drill chart and teach you how to use it. ![]() Add in some potentially complicated sizing systems, and even a simple tap drill chart might require some explanation. But to a newcomer, they might not appear to make a whole lot of sense. Tap drill charts are a machinist’s best cheat sheet and how-to guide all in one. MX Electric Edge Finder and Z Axis Touch Plate.CNC 1440 Lathe Benchtop Turning Center Catalogue.– CNC SUPRA® Vertical Knee Mill 9 x 49 or 10 x 54.
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