When mounting a router into a router table or positioning a guide bush accurately in a router base, some sort of centring device can be a really useful aid. The Bosch Centring Cone is an excellent aid for accurate set-up. The cone is supplied with two interchangeable shafts which have a different diameter on each end. This allows fitting to a range of collets to suit your router. They will fit the following sizes: 1/2"(12.7mm), 1/4"(6.35mm), 8mm and 12mm.