Door handle is an ambiguous term, and includes door latches, bars, and knobs. Depending on the geographical location and its place in time, they vary in design, form and materials. The only constant is its function: an attachment used to open or close a door.Knobs and handles functionsThe earliest doors extant are approximately 5000 years old. Door handles, as devices to manipulate a gateway, became a necessity shortly after the invention of the pivoting mechanism. To most, pivots are simply known as hinges, however, there are nearly as many hinge designs and configurations as there are handles.The simplest handle is a pull - or push - projection on the side opposite the hinge. The placement of the handle is generally where it will provide an optimal mechanical advantage; most stainless lever door handle for saleoperating as second class levers. Doors with centre pulls or rings, or a pivot point in a location other than one edge of the door, use first or third class lever principles.Depictions of door handles in paintings dating to the first century CE are centrally placed hinged rings. The modern door knocker is a vestige of this style of primitive door handle. Doors were typically secured by bars and brackets to prevent them from being opened by either intent or accident.Knobs with latches and barsOver time, large crossbars used to secure a door were supplanted by sliding bars, operated by a handle secured to the bar and projecting through a slot in the door, or as a pivoting bar - often called a latch - that could be dropped into a matching slot on the door jamb. In Colonial America, the operating mechanism for a small pivoting bar was a latch string threaded through a hole in the door near the handle. There are - probably apocryphal - accounts and references implying that this mechanism was a workaround for heavy taxes and a crown edict mandating the colonists could only use door latches or locks imported from England.