Message text written by "Tony Zanussi"
> What are the actual taps and dies I need for most bike related threads?
Dimensions? Corresponding drill bits?<<<<<
There are skads of tap and die sets on the market and while most of them will contain sizes not usually found on bicycles, the whole set is usally cheaper than buying three or four individual items. Some sets are either metric or SAE only while others have both. For modern bicycle use, the metric only is what you need. Now as to the corresponding drill size, that becomes a bit more difficult. You need to drill a hole the size of the bottom of the threads. Such information is readily available in machinist's handbooks for SAE but I've never seen it for metric. That certainly doesn't mean it's not available. Lacking a chart, the way to get this drill size, you take the pitch of the threads, double that and subtract that number from the size of the tap. Since I was raised with and relate to inches, I simply convert the numbers. Take the M 5 X .9 size. That means that the outside diameter of the screw is 5mm (.200") and the thread pitch is .9mm (.036"). Double that and you have .072". .200 - .72 = .128". Since that is only slightly off being 1/8", you can use that size drill bit. However, on other metric sizes which are nowhere near a common fractional size, you will need a set of letter or number drills to find the proper size. Just don't forget to use a good CUTTING oil when you tap or cut threads. If you don't, you will likely mess up both the threads you are cutting and the tap or die you are using.
Jim