in Europe and the Americas during the late 19th and early 20th century. Slip joint knife 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 Industrial Revolution and development of machinery capable of mass production. Many locking knives have only one blade that is as large as can be fitted into the handle, because the locking mechanism relies on a spring-loaded latch built into the spine or frame of the handle 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: Multi-tool knives Multi-tool knives formerly consisted of variations on the American camper style or the Swiss Army knives manufactured by Victorinox and Wenger. However, the concept of a multitool knife has undergone a revolution thanks in part to an avalanche of new styles, sizes, and tool presentation concepts. These new varieties often incorporate a pair of pliers and other tools in conjunction with one or more knife blade styles, either locking or nonlocking. Multitool knives often have more than one blade, including an assortment of knife blade edges (serrated, plain, saws) as well as a selection of other tools such as bottle openers, corkscrews, and scissors. A large tool selection is the signature of the Swiss Army Knife. These knives are produced by Victorinox and Wenger and issued to military services and sold to the public. Similar to the Swiss Army knife is the German Army knife, with two blades opening from each side and featuring hard plastic grips and aluminum liners. The U.S. Military utility knife (MIL-K-818), issued by the United States Army, Navy, and Marine Corps, was made for many years by the Camillus Cutlery Company and Imperial Schrade as well as many other companies. It was originally produced with carbon steel blades and brass liners (both vulnerable to corrosion), but with the onset of the Vietnam War was modified to incorporate all-stainless steel construction. The current-issue U.S. military utility knife has textured stainless grips and four stainless blades/tools opening on both