The 5 inch Dual Action Backing Plate is designed for polishers with a 5/16 inch spindle. This includes the Porter Cable 7424XP. The 5 inch Dual Action Backing Plate features durable hook and loop backing. This backing plate is compatible with our 5.75 inch Redline Foam Pads. By equipping your dual action polisher with a 5 inch Dual Action Backing Plate, you greatly expand the capability of the machine by having the ability to polish body panels of all sizes.