This is an OEM part sourced directly from the manufacturer. The knob is used in several models of Graco sprayers. This is a high-quality plastic knob with a threaded metal interior, and is generally used to help hold the handle of the machine to the frame. In order to replace this part, you may want to use a screwdriver to hold the scr...Read moreew in place while you unscrew the old part and thread the new part into place. This item is sold individually.