Clamping apparatus for confining and maintaining electrical contact with multiple longitudinally extending rib wires during the resistance welding thereof to wire wrapped thereon for forming a well screen or the like, wherein the clamping apparatus compensates for wear thereon. The apparatus may be automatically adjustable for wear and also variable in diameter to permit forming the welded screen on upset tubing and on other pipe having variations in the outside diameter thereof while still effecting the electrical contact required for reliable and sound resistance welding of the multiple rib wires to the wrapping wire.