The ST 84 S is an invaluable set in a small package. When holes must be drilled with precision through the center of a shaft, you must get a perfect start at the center. These center drills are specially designed for that purpose. Once the center drill has started the hole, your standard drills will follow. 4 drills are included, each double ended, giving you 8 cutting tips in all. Sizes are 1/8", 3/16", 1/4" and 5/16". The angle is standard 60 degrees and allows you to use them for making countersinks as well.