Abstract: A distortable diaphragm seal, which is preferably formed of felt, seals each end of a nut through which a screw extends. Grease, which is introduced into the interior of the nut to function as a lubricant, is sealed therein by the seal. The seal has an opening of substantially the cross sectional shape of the screw normal to the axial centerline of the screw to permit part of the seal to extend circumferentially along the unthreaded O.D., and to permit another portion of the diaphragm seal to run into, and out of, a helical groove in the ball screw, thus forming a continuous seal on the screw surface.