3M(TM) Shoe Electrode 741 3M(TM) Shoe Electrode 741 is a test plate that connects to the 3M Wrist Strap and Footwear Tester740 to test heel straps. By standing on the 741, personnel can use the 740 to check the operation of static control footwear, heel straps and the like. This electrode, constructed of rugged stainless steel in a molded plastic base, must be ordered separately.