3” X 4” Soft Interface Pad (Grey) With 6 Holes for Vacuum 1/2" Thick We recommend using a J-Hook Backup Pad when sanding with any Interface Pads. This is because the interface pad will not stay in place while sanding using a standard Hook and Loop backup pad, whereas using a J-Hook backup pad will allow the interface pad to stay in place. https://youtu.be/FxkWyzcbUNc