the workpiece size: from 7mm to 19mm.(1/4"-3/4") the material : CR-V material spec: 5.2cm length with 54pcs steel wire. grup socket wrench is based on pin-locked principle. thers a spring installed in each pintail and neednot be adjusted. you can assemble flatshaped, square-shaped, hexagon-shaped and other shaped objects with friction in the range of 7-19mm(1/4"-3/4")freely, this tool is cold-forged with special crvb alloy steel. its small volume, beautiful shape, reasonable structure, advanced technology, excellent quality,its precision, torque all reach international standard. it can be applied widely in maintenance of automobile, motorcycle, mechanical manufacture, equipment installation and other civil fields. its a commmonly used tool for enterprises and you may prepare for family if you need.