How Do I Use a Tap & Die Set? News & Opinion

How to Use a Tap and Die Set


When using a tap and die set, it’s important to understand the terms. “Tapping” is when you cut, or recut threads into a hole or nut. Anyone who has worked on vehicles long enough has likely dealt with this issue in the form of a stripped socket or cut off bolt which has to be re-threaded. Learning how to use a tap and die set gives you a way to fix serious problems in metal that would otherwise leave you high and dry.

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How to Use a Tap and Die Set

You use a “die” to cut or repair threads onto a bolt. Before you can start spinning away, you first have to determine the number of threads per inch (TPI) in either the bolt or the nut. Most tap and die systems, include a gauge that has a number of different “blades” which can be used to calculate the TPI of a bolt or nut. It often looks a little like a small pocket knife. After determining the TPI of a bolt, you can then select the die that corresponds to it. Keep in mind that these sets come in both metric and SAE, and sets can be small or extensive in size. Both taps and dies are tapered so that they can ease into a bolt or nut and gently re-carve the threads as they were intended. The dies fit into a special wrench that holds it fast, giving it leverage to spin it around and guide it on its cutting path.

Fixing Threads with a Tap and Die Set

If you were using the die to fix the threads on a bolt that had become cross-threaded, you would need to secure the bolt, something you can accomplish by using a vice – just be careful to not further damage the threads. It helps to position the bolt in the vice such that it is not grabbing onto any threads you intend to use. Carefully align the die so that you don’t go down on an angle, but straight down the bolt. When you begin to rethread the bolt it may start to heat up – something that is inevitable when tightly rubbing two metals together – and it’s more apparent when you engage in longer thread lengths. We recommend you use a little cutting oil to lubricate the die and keep it cool during use. Since most tap and die wrenches have an open top, this is pretty easy to do without having to remove the die. This also extends the life of your tap and die set.

When you’re learning how to use a tap and die set you’ll begin to get a feel for the process quickly. As you thread the die down onto the bolt you will feel it quickly begin to catch. Every few turns you may have to back the die out a bit to clear the threads and allow it to cut better. This is to be expected and is akin to drilling into wood with a large bit. Once the die makes it far enough down that the bolt sticks through the top you will know you are finished.

Rethreading with a Tap and Die

Using a tap to thread (or re-thread) a nut is just as easy. If doing this apart from a matching bolt you would use the gauge to select the correct size for the nut or hole you wanted to thread. For those doing a nut on its own, you would want to use the actual matching bolt to set the size, keeping you from needing to try and muscle the gauge into a worn out bolt (or based on its location, this may be impossible). Also, if the threads are completely damaged, the other solution is to drill out the hole and re-tap it for a slightly larger bolt size, or even fill it and re-tap it.

To begin, place the tap into the provided wrench and secure it. Next, place the tap into the nut and begin turning it down by hand – being cautious to keep it perfectly straight to the hole. As with using a die, adding oil is a must and you will need to back it out frequently to get rid of debris that builds up in the threads.

That’s all there is to it. Using a tap and die set can really remedy some nasty situations and it’s the kind of tool that not everyone will need – but when you do there is no other substitute.

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