Wrenches commonly referred to as sleeve: it is composed of a sleeve with a hexagonal hole or a plurality of second corner holes and equipped with a handle, extension bar and other annexes, especially for small or twisted position is very deep depression at the bolt or nut. Sleeve metric and imperial points, although the sleeve concave shape the same, but the outside diameter, and length of the corresponding device for the shape and size of the design, the state is no uniform requirement, so the sleeve design is relatively flexible, meet the needs of the public. http://www.hbbtglj.com/tzbs/