Most pocketknives for light duty are slipjoints. This means that the blade does not lock but, once opened, is held in place by tension from a flat bar or leaf-type backspring that allows the blade to fold if a certain amount of pressure is applied. The first spring-back knives were developed around 1660 in England, but were not widely available until the arrival of the Industrial Revolution and the development of machinery capable of mass production. Most locking knives have only one blade that is as large as can be fitted into the handle, because the locking mechanism relies on the spring along the back of the blade to lock it and it is difficult to build in multiple levers, one for each blade. Slipjoints tend to be smaller than other typical pocketknives.
Some popular patterns of slipjoint knives include: