Tap sizes

There's diameter and thread pitch.

So a 10 x 1 is 10 mm diameter x 1 pitch and 10 x 1.25 is 1.25 pitch.

https://www.carrlane.com/en-us/engineering-resources/technical-information/design-standards-and-engineering-information/inch-and-metric-thread-standards

There was an old metric standard - everything on a bike is likely to be the newer I.S.O.

There's all sorts of learned magic associated with cutting and chasing threads, and there are different sorts of taps, e.g. a bottoming tap. If you wade in blind you're quite likely to do more damage than good.

generally when the threads strip of of those components you're not going to be able to just re-tap them as the material is lost, which increases the ID. you'll most likely need to use a helicoil, which is really only a temporary solution.

A properly installed Heli-Coil is stronger than the original threads...

Taps are available at any industrial supplier. Better to buy what you need when you need it than to stock with tools speculatively. Learn what a tapping block is and how to use it.

maddog17 said:

so I'm thinking of adding a few taps..

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start here and work your way up...

WestCoastHucker said:

start here and work your way up...

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I would fap to that.

maddog17 said:

so I'm thinking of adding a few taps to my tool box for the just in case scenario. so I'm a little confused on what to get for sizes. I'm thinking one for pedals, rear drop for der. and maybe water bottles. so looking at Park, they have a 10mm for rear der. and it's listed as a 10 x 1. so if I look at Harbor Freight, they offer sets but the sizes are bigger than 10 x 1. they list in their kits as 10 x 1.25 and 1.5. so is Park at a true 1mm or is it larger like whats offered at HFT.

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johnbryanpeters said:

Taps are available at any industrial supplier. Better to buy what you need when you need it than to stock with tools speculatively. Learn what a tapping block is and how to use it.

Click to expand...

I would agree to just buy taps as you need them. However many bike threads are non standard and bike specific and can be harder to find, which is why a standard tap kit won't have them. For example:
As you found, the rear derailleur mounting screw is M10 x 1. M10 x 1.5 is the common coarse size, and M10 x 1.25 is common fine size for screws.
Pedal threads are 9/16 x 20 TPI. The most common screw size close to that is 9/16 x 18 TPI fine thread, and coarse thread is 9/16-12.

Park has a good breakdown of bike related thread sizes: https://www.parktool.com/blog/repair-help/basic-thread-concepts

Luckily there is a bike shop in my town that lets you borrow tools to work on your bike, so when I needed to chase the pedal threads on my SLX crank I was able to just stop by there and do it. My GF also had a stripped out M5 rack boss on her CX bike, so we just drilled the bosses out and re-tapped to M6 instead.

I have been using this for about 2 years now. I am a professional mechanic so mine gets used much more than a home one would. All the taps are still good even the M5x.8 (water bottle and fender mounts). I bought the kit to keep on my bench so I didnt have to go to the shop tap kit every time. I didnt have any expectations going in but I have to say I am impressed. Icetoolz Part number E158