Drill Tap Bits

Jul 05, 2023

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Don’t settle for drilling in metal only to get poorly threaded holes or broken bits.

The average do-it-yourselfer hates to drill metal, especially steel. We don’t know how many questions readers have submitted and we’ve answered on that topic over the years. Even the most enthusiastic handy-person merely gets through it as best as he or she can. Tapping metal (cutting internal threads in a hole) so that you can thread a bolt into the hole is still more difficult–though it shouldn’t be. People avoid it or struggle through with ill results, like poorly formed threads or a tap that snaps off in the hole before the job is done.

But all that’s changed with the advent of an accessory called a drill tap. It’s a form of bit that combines a drill and a tap, making a hole and threading it in one easy operation. And it’s changed metal working for do it yourselfers and professionals alike. What follows is a quick explanation of the drill tap. Scroll down to the bottom for advice on best practices and our buying guide.

Tapping a hole means cutting internal threads in it so it can accept a bolt or threaded fitting. It was once a labor-intensive process. It would require a drill, a drill bit, an accessory called a tap, and a tap wrench. First you ensure that you’ve selected a drill bit sized to match the tap by consulting a drill-and-tap chart. Next, you tighten the bit into the drill, then take the tap and tighten it into the tap wrench. You drill the hole, then lay the drill aside and use the tap wrench and tap the hole (that is, cut the threads in it). To do that, you carefully twist the tap in; it will wobble a little at first so you have to keep it upright while applying steady downward pressure. As the tap makes a little progress, you reverse the wrench to break the metal shavings that are accumulating in the tap’s threads. These shavings can prevent the tap from making progress; they can even get the tap stuck in the hole. Also, if you used the wrong size drill, that will certainly cause the tap to get stuck. In either case, you stand a chance of snapping the tap off in the hole, and extracting a broken-off tap is no small job.

Picture this alternative. Tighten the drill tap into your drill, then drill and tap the hole in one fast and easy operation. Done. What took minutes before takes seconds now. And because the drill and tap are combined, you can’t get the size of the drill wrong. This eliminates the risk of getting the tap stuck in the hole.

There are several secrets to the drill tap’s success. First, it’s made from incredibly tough high-speed steel that easily cuts a thread in all but the toughest materials. It also works well in both ferrous and non-ferrous metals.

Second, the drill tap’s geometry cancels out problems that may occur in tapping a hole. Its tip is a conventional drill bit, and the tap threads begin gradually behind the tip, come to full height, and then taper off. This back taper prevents damage to the threads you’ve just made. In other words, once the accessory cuts the threads, the part of the bit that follows doesn’t touch them.

This 13-piece set is unusual in that it contains six metric (M3-M10) and six SAE (No. 6-10 and 1/4-20) bits, plus a quick-change bit holder.

DeWalt's five-piece set covers common sizes. The bits are specifically rated to withstand use in an impact driver.

Greenlee provides six common sizes of drill taps and a quick-change bit holder in this seven-piece set.

If you already own a set of SAE drill taps, you can augment them with this five-piece metric set in M4, M5, M6, M8, and M10 sizes rated for both impact drivers and drills.

When drilling metal, even soft metals like aluminum, I always start the drill on a mark I created with a center punch struck with a ball peen hammer. The indentation that creates prevents the drill tap from slipping off where I need to make the threaded hole.

Although drill tap manufacturers make no mention of the need for lubricant, I always use it. I’ve found it not only makes for easier drilling (on me, the drill tap, and my cordless drill), it extends the life of the drill tap. My favorite lubricant is Relton’s Rapid Tap. A few drops is all it takes in steel or aluminum to ensure you get a clean, rapidly tapped hole.

Use a can of spray lubricant and a plastic parts brush to clean metal shavings out of the newly tapped hole. In fact, you might even use the parts brush to knock any metal shavings off the bit before reversing it and backing the tap through the hole that you just threaded. That can prevent damaging the threads you just cut.

Using a cutting fluid reduces friction and helps extend the life of a drill tap. This in turn cuts down on the likelihood of a tap snapping off.

To be sure that the drill tap starts where you want it, mark the location with a center punch struck with a ball peen hammer.

Clean metal shavings out of the hole and off the drill tap itself using a brush with plastic or brass bristles.

Blast fine metal particles out of tapped holes and lubricate the fastener before driving it in using WD-40.

Roy Berendsohn has worked for more than 25 years at Popular Mechanics, where he has written on carpentry, masonry, painting, plumbing, electrical, woodworking, blacksmithing, welding, lawn care, chainsaw use, and outdoor power equipment. When he’s not working on his own house, he volunteers with Sovereign Grace Church doing home repair for families in rural, suburban and urban locations throughout central and southern New Jersey.

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