By closing the opening in the base of your router to match the diameter of smaller bits, you will reduce the risk of getting small pieces of wood between the bit and the plate opening. This lessens the chance of kick back while running your router. The bushings also provide support for smaller work pieces, increase dust collection efficiency and help reduce tear-out. The bushings will fit router bases or router table inserts with a standard 1-3/8" diameter - recessed opening that accepts template guide bushings. Each bushing will accept a router bit that is at least 1/32" smaller than the bushing size. Example: the 5/32" bushing will accept a 1/8" router bit.