The Two most common types of spacers are the Round spacers with the Hexagon spacer is also used in many applications as well. Spacers are not threaded and are used primarily in minimum clearance space requirements. "Threaded spacers are known by another name, “Threaded Standoffs” which are basically a threaded spacer. Spacers are used to keep two components at a given distance from each other. A screw is inserted through the inside diameter of the spacer to a threaded component or nut (female end).