Jaws adjust to tightly secure taps from #6 to 1/2" taps. 3/8" square drive compatible with common ratchets. Small profile for use in tight workspaces. Knurled ring twist to adjust for quick fit. 2 piece set for greater versatility Both adjustable tap sockets are 3/8" drive, one fits #6 through 1/4" taps and the second adjustable socket fits 1/4" through 1/2" taps. This Irwin innovation allows the easy use and changing of various sizes of taps.