The chuck includes a 23/64 drill bit for drilling the hole that the stopper stud screws into. (Note: Using the chuck requires drilling the 23/64 hole then threading in the stud. Threading wood into a wood or acrylic hole is not an exact science; you may find the mandrel a bit too loose or too tight depending on many factors including; your drill press accuracy, type of material, moisture content etc. Although the bit works fine in most cases we cannot guarantee it works in all cases. For best and most consistent results, use Drill and Tap set #BSTAPSET. This set includes a 5/16in drill bit and 3/8in tap that will work perfectly every time regardless of materials).