Permanent, ceramic magnets for superior holding power, never lose their strength. Back surface of the aluminum chuck body has tapped holes and turned counterbore for convenient mounting on machines. All models except 5-1/4" dia. which uses the swing-type on-off method, are watertight. Standard Pole models have 1/4" poles and 1/8" separators.. Picture Shown: Model No. RMC-6, 6-1/4".