FLEX XC3401 4 Inch Changeable Backing Plate System The FLEX XC3401 4 Inch Changeable Backing Plate System by Lake Country allows you to change to a 4 inch backing plate using a specially designed gear plate. You can use every size pad from 4 inches to 5 inches with this two-piece system on your FLEX XC3401 VRG Orbital Polisher. Now you don't have to buy a specific backing plate for each size pad - the FLEX XC3401 Changeable Backing Plate System works for the most common sizes.