In use, the outside of a guide bush acts as a fence, limiting the distance between the work and the cutter’s edge. The UJK guide bushes are a precision router accessory, CNC turned from stainless steel. Their outer diameters range from 12mm to 30mm with 6.5mm projection (101875 (30mm o/d) has a 10mm projection suitable for kitchen worktop jigs). All these guide bushes fit into the near standard 60mm diameter recess found on Elu, DeWALT and Trend routers plus many more. Fitting a UJK universal sub base solves the problem for routers with different base configurations.
The cutter runs in the centre of the bush and the outside edge of the bush rubs against the template determining the position of the cut. Knowing the diameter of the guide bush and that of the cutter you can work out the offset required when making a template. To calculate the offset, take the guide bush diameter, subtract the cutter diameter and then divide that figure by two. Remember, when routing around the outside of a template move the router anti-clockwise and when routing around using the inside, move your router clockwise.