Make no mistake: having a good drill bit size chart (sometimes called a “drill index”) is a very handy thing indeed to have around. If it has information on which twist drill size to use for tapping, so much the better. But in this age of computers and the Internet, you can do better. Newsflash: There Isn’t Just One Drill Bit Size for a Tap Well, you can’t use a standard drill chart, that much is clear. You could calculate the optimal size for a particular percentage of thread and then go to a standard drill chart to find the nearest size. That works, but it is a fair amount of trouble.

So what’s the right way to choose a thread percentage and how do we get from there to a proper drill size? General Guidelines for Choosing Thread PercentageSo go ahead, give G-Wizard free trial, a try. You’ll be surprised at all the time it saves you on things like Tap Drill Sizes, not to mention the longer tool life, better surface finish, and shorter cycle times you’ll get from better Feeds and Speeds. Bonus: Depth Clearance When Tapping Blind Holes Total Tools reserve the right to change or withdraw free delivery at any time. Estimated Delivery Timeframes Nice, huh? It saves people a lot of time. There’s a whole ton of other very handy reference time savers there too, not to mention the world’s best Feeds and Speeds Calculator. I’ve all but quit having to dig through my Machinery’s Handbook to find information–I just use G-Wizard.

Special event, club or membership offers, third party promotions or prices not available to the general public Let’s start with an important fact–there isn’t just one drill bit size to use for a given tap size. There are several. Moreover, the size recommended in most drill bit size charts is very often not the best size to use. The same is true of the size recommended on the tap and even the recommended size from the tap manufacturer. Anytime you see just one size being recommended, you know you can do better–one size does not fit all when it comes to tapping. How can that be? Well, it’s actually pretty simple. To know which drill bit size is right for your particular tapping application, you need to consider what thread percentage you want when you’re done tapping. What’s Thread Percentage and Why Care? As a rule of thumb, for Metric threads, the tapping drill can be calculated by subtracting the pitch from the diameter of the thread. eg for an M5x0.75 thread the tapping drill is 5-0.75mm = 4.25mm. But, before you do, wouldn’t you like to hear about something that’s much better in every way? Something that’ll make it much less likely you’ll break a tap? Something a little more modern than a simple chart?

ENQUIRY FORM

In fact, the main disadvantage of Form Taps is they can’t be used on materials that are too hard. The hardness limit for Form Taps is higher than you probably think (they’re good for much more than aluminum), but there is a limit nonetheless. Given all that, you’re definitely going to need to figure out Form Tap Drill Sizes too! Better Thread Gaging. Form taps work by cold forming the metal in the hole. Since no chips are made, the likelihood of producing oversized threads is far less than for Cut Taps.