I quickly calculate proper tap-drill diameters using this simple formula. Tap-drill diameter equals nominal diameter minus thread pitch. For example, drill size for a 3/8-16 thread is 0.375 0.0625 ...

I'm trying to figure out which type of bit is best for drilling thru about 1/4" of galvanized steel. I recently used a standard carbon-steel bit to drill thru the steel. While the bit was able to ...