The job of a spacer is simply to let a bolt pass through it in order to separate two objects. The two objects are fastened by the bolt and nut, but separated by the spacer. The difference between a spacer and a standoff is that the inside of a spacer is not threaded. Our offerings of round spacers vary by length, material, screw size, outside and inside diameter and other dimensions, color, and finish, among other considerations. For standoffs, see our hex standoffs, square standoffs, and slot mount standoffs.