Bench dog hole drill bushing
These 3/4" and 20mm hardened steel bushings help you make an accurate dog-hole drilling guide using any 1-1/2" thick board. Knurling on the bushing provides a mechanical lock when installed in an appropriately-sized hole (1" for the 3/4" bushing, 25mm for the 20mm bushing), and a projecting rim ensures that it rests perpendicular to the jig’s surface. If you don’t already have a bit in the required size, Lee Valley offers 1" and 25mm high-speed steel forstner installation bits that are 3-1/2" long overall.
For drilling the dog holes, Lee Valley offers 3/4" (#07J02.48, $33) and 20mm (#07J16.20, $35) drill bits that are 6" long overall with 3-5/8" of fluting, enough to go through the jig and a 2" thick bench top. The lipped brad-point style scores the perimeter of the hole for clean entry and smooth sidewalls. Made from high-speed steel, they are long lasting and not subject to burning.