METRIC WHEELNUT FASTNERS INFORMATION

** THESE ARE NOT INTERCHANGEABLE WITH CUSTOMARY (INCH) WHEEL NUTS AND STUDS. IF ONE IS FORCED ON AS A REPLACEMENT FOR THE OTHER, DAMAGE TO THE STUD/NUT THREADS WILL OCCUR, WHICH COULD ALLOW THE WHEEL TO COME OFF WHILE THE VEHICLE IS MOVING, POSSIBLY CAUSING LOSS OF CONTROL, PERSONAL INJURY, AND PROPERTY DAMAGE. WITH THE EXCEPTION OF CHEVETTE AND T-1000, METRIC WHEEL STUDS WILL HAVE THE LETTER "M" STAMPED INTO THEIR THREADED END AND THE WORD "METRIC" ON THEIR HEAD (SEE FIGURE 1). METRIC WHEEL NUTS ARE BLUE IN COLOUR AND HAVE THE WORD "METRIC" STAMPED INTO THEIR FACE, WITH THESE EXCEPTIONS: - EARLY MODEL YEAR CHEVETTES - CAPPED OR CHROME STYLED NUTS ALL METRIC WHEEL NUTS ON GM CARS HAVE A THREAD SIZE OF M12X1.5 AND REQUIRE A 19 MM (OR 3/4 INCH) SOCKET. CUSTOMARY (INCH) WHEEL NUTS CAN HAVE A THREAD SIZE OF EITHER 7/16-20 OR 1/2-20, REQUIRING A 3/4 INCH (OR 19 MM) SOCKET OR A 13/16 INCH SOCKET, RESPECTIVELY. THE CHART ON THE FOLLOWING PAGE SHOWS GM'S CONVERSION TO METRIC WHEEL NUTS BY CARLINE. ALUMINUM WHEELS: ON GM CARS WITH ORIGINAL EQUIPMENT ALUMINUM WHEELS, SPECIAL STYLED WHEEL NUTS ARE USED. ALL GM CAR MODELS PRIOR TO 1982 USED A SOLID CHROME FLANGED NUT (FIGURE 2-LEFT). DURING THAT PERIOD, THE NUT COULD HAVE HAD EITHER METRIC OR CUSTOMARY (INCH) THREADS, DEPENDING ON ITS GM CAR MODEL USAGE. BEGINNING WITH THOSE 1982 GM MODELS MARKED WITH AN ASTERISK (*) IN THE CHART, METRIC THREAD CAPPED CONICAL NUTS ARE USED (FIGURE 2-RIGHT). THE 1982 SEVILLE, ELDORADO, AND RIVIERA CONTINUES TO USE METRIC CHROME FLANGED NUTS. THE 1982 LESABRE, ELECTRA, AND CORVETTE CONTINUES TO USE CUSTOMARY (INCH) CHROME FLANGED NUTS. CAUTION: TO REDUCE THE RISK OF A WHEEL COMING OFF WHILE THE VEHICLE IS MOVING, POSSIBLY CAUSING LOSS OF CONTROL, PERSONAL INJURY, AND PROPERTY DAMAGE, DO NOT USE A FLANGED NUT IN PLACE OF A CONICAL NUT OR A CONICAL NUT IN PLACE OF A FLANGED NUT. CONTACT SURFACES ON THE WHEEL ARE DESIGNED DIFFERENTLY TO ACCOMMODATE THE DIFFERENT DESIGN NUTS (SEE FIGURE 2). BOTH OF THE ABOVE STYLED NUTS CAN BE USED WITH THE STEEL SPARE WHEEL (SEE FIGURE 3).

General Motors bulletins are intended for use by professional technicians, not a "do-it-yourselfer". They are written to inform those technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions and know-how to do a job properly and safely. If a condition is described, do not assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See a General Motors dealer servicing your brand of General Motors vehicle for information on whether your vehicle may benefit from the information.