This bridge pin hole drilling jig was developed by Frank Ford. It allows you to drill accurate holes in your bridge at whatever stage you want, whether in the wood blank or in the finish sanded bridge. It's essential to get the holes accurate - nothing looks worse than a replacement bridge with uneven pin holes! I've used one of these jigs in the workshop for quite a few years. Holes are accurately located for 2 1/8", 2 1/4", 2 5/16" or 2 3/8" spacing. The jig comes with an alignment pin and an Allen wrench. The top is machined from hardened steel for long life. Hole spacing on this tool is equidistant, there is no compensation for string gauge. This tool is set up for 3/16" bridge pin holes.