Features and Benefits:?Custom sizing: Use with Milwaukee Thin Wall 3-1/2" Core Bit (48-20-5050) and centering pin (48-20-6155)?Increased drilling precision: Reduces bit walk and improves bit stabilityUse for starting a 1-1/4 in. hole drill to a depth of approximately 1/4 in., stop hammer, remove guide plate and center pin. Place core bit back into the grooved area and resume drilling to required depth of hole. Adds bit stability and reduces bit walk.