In foodservice equipment, a knob may be as simple as a push button or palm button. A control knob is a rotary control used to provide input to a device when grasped by an operator and turned, so that the degree of rotation corresponds to the desired input . Such knobs are one of the most common components in restaurant equipment control systems and are used to modulate a wide variety of settings such as temperature, viscosity, speed and more. Specifications. Height 2.2 in.. Width 3.15 in.. Length 3.1 in.