Eliminate the chance of your drill bit popping through the drywall! This Rack-a-Tiers Bumper Ball set keeps your drill bits centered and stops them from "bit walking." Rack-A-Tiers Bumper Ball Set helps guide your flexible in-wall drills to their correct location without having them go off course. This set includes two different sizes that fit most 3/16" shaft drill bits. The two included ball diameters are 2-1/4" and 1-3/4". Features: Keeps Your Drills on Course Centers Drill Bit Between Walls Reusable Specifications: Kit includes 1 each of 1-3/4" and 2-1/4" balls Fits all 3/16" shaft auger bits Drill bits not included