Vac-Pad works exclusively with the Model HMD904 & HMD905 on non-ferrous materials, diamond plate and materials with surface imperfections up to 3mm deep. Standard shop air provides 761 lbf surface holding power at 85kpa. Safety switch shuts off drill motor if air pressure drops. (For HMD904 & 905s with taper back magnet and non-swivel base models only)