7 RESISTANCE WELDING MACHINES, WELDING PRESSES, MACHINES FOR PERFORMING WELDING OPERATIONS, PARTICULARLY, ON PARTS OF MOTOR VEHICLES, HOUSEHOLD APPLIANCES AND RADIATORS; FRICTION WELDING MACHINES; HAND-, MECHANICALLY- OR HYDRAULICALLY-OPERATED AUXILIARY DEVICES FOR HOLDING PARTS TO BE WELDED; ACCESSORIES-NAMELY, ROLLER BLOCKS AND SUPPORTS FOR AUTOMATIC WELDING MACHINES