This is a 6 piece set of coarse thread rethreading taps including: 1/4"-20, 5/16"-18, 3/8"-16, 7/16"-14, 1/2"-13 and 9/16"-12. These are all very common sizes. In most situations they will clear away rust and dirt or straighten out threads that have been damaged. The benefits of using these instead of a regular cutting tap are: less expensive, convenient hex drive that will fit in your socket set, shorter than most taps for hard to reach areas, won't undercut threads, and they are less brittle. Each tap has the size stamped into it and they come in a vinyl pouch. Use these and keep your thread cutting taps sharp for when you need to make new threads! mstc part# T6C * MADE IN THE USA*