a pair of o rings 32 and 33 are provided for fluid tight seals between the wall structure and the piston and rod 30 and 31 respectively at the one end of the cylinder 29 an adjustable stop 34 having a lock nut 35 is threadedly received in the housing 14 to contact the piston 30 a pair of pressure lines 36 and 37 are connected from a source of pressure not shown into the conduits 25 and 26 respectively and an outlet fluid line 38 serves to connect the conduit 28 with the spray device 16 referring now to fig2 and 3 taken in conjunction with fig1 the spray device 16 includes a metal block which is attached to related structure of the welding apparatus 10 by means of a pair of threaded fasteners 39 and 40 and a stud holding collet 41 extends from the nozzle 18 of the welding gun 20 through an opening in the block a flash shield 42 of metallic material is retained in the spray device 16 by a flange 43 in spaced relation with the collet 41 the collet 41 retains the metallic stud s adjacent the workpiece w as shown in fig1 and the relationship of the flash shield 42 collet 41 stud s and workpiece w during the welding operation is similar to the relation of these elements.