These special wooden-handled steel reamers are designed to properly taper the holes for bridge pins. They're semi-fluted, to help keep the holes round. This 3-degree reamer tapers from approximately .312" to .150", and is suitable for many bridge pins from Gibson and other high end makers, including Martin pre-1994 and Collings pre-2002. (Slightly) cheaper versions can be found, but these are the best way to ensure accurate fitting. Please note that handle wood and colour may vary.