I've got to tap a few holes for some stripped bolts i have on my 2000 cav. I know i have to use a tap to create the threads. I have a tap and die set but was unsure what the screw pitch gauge is and when i would use it?

Also,

what is the difference between "nominal size" and "tap drill size" How do i know what size drill bit i need to use for teh correct tap?


Ryan1

Well, you match the thread pitch to the pitch of the threads on the bolt that will go into the hole with the pitch gauge. You can also tell by taking the same size/pitch die and threading the bolt into it. This tells the correct pitch and size tap to use for the bolt you are going to use.

As for the correct size bit, I match the bit up by holding the two together, the drill should be as wide as possible without being as deep as the threads if that makes sense. The tap needs to have material to cut out for the threads.





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I take the tap size and find the corresponding nut. Then find the biggest drill bit that will still pass through the nut.

^ I think that would be the best way to get the correct drill bit. As for the thread pitch guage, if it is one with a bunch of "serated blades" that fold out like a pocket knife, match the serations up with the threads of the bolt. All of the serations have to fit into the threads, not just a few. If you don't know wether the bolt is metric or SAE, try both and pick the closest fit. I typed a little more information in your other thread, i don't feel like typing it twice.

I hope this is understandable. I'm not the best at explaining things.



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The best way to get the correct sized bit is to grab the Decimal Equivelency chart that probably came with the Tap & Die set, look up you thread size and pitch and the next column will probably say "Drill Size" - that is the correct size. Remember to get it straight and use anchor lube, and break the chip every turn.