The 9921 Adapter Washer Set allows you to use an 8-32 (M4) screw to mount something that is fitted for a larger 1/4-20 (M6) screw. The washer's outer diameter is sized to match the diameter of larger 1/4-20 (M6) screw head. Its inner diameter is sized to clear an 8-32 (M4) screw shaft. Set of 25.