The purchase of a complete set of numbered and lettered drill bits is perhaps the best tool investment I ever made. The numbered go from #1 - 0.2280 to #60 - 0.0400 and A - 0.234 to Z - .0413. I bought the set along with a standard 1/16" to 1/2" bits in a case for under $20 at Harbor Freight. It was a special sale, and you might have to wait for another.