Gearwrench 81602 41 Piece Master Ratcheting Wrench Insert Bit Set. Concept from users cutting Allen keys and using in ratchets to access tight spaces. Compact height and narrower body than regular ratchet & socket or bit socket for access. Fits into existing ratcheting wrench, 8mm, 12mm, 15mm. Can also fit in a socket and be used like a nut driver.