They are manual tools created to apply greater torque to a nut, without being able to change the opening of their jaws to adapt to the size of the nut to be tightened or loosened. They can be open-mouthed, u-shaped, or well-closed, o-shaped. When they are closed keys with a cylinder shape of greater or lesser height, they are called socket keys. When combined at one end open type and the other end closed type, they are called combination wrenches.