For service and parts needs, visit your dealer. You will receive genuine GM parts and GM-trained and supported service people.
Genuine GM parts have one of these marks:

Vehicle Care
California Proposition 65 WarningInstallation Procedure
Note: If the location of the original plug weld holes can not be
determined, space the plug weld holes every 40 mm (1½ in).
Drill 8 mm (5/16 in) for plug welding along the edges of the body rear
end panel as noted from the original panel.
Clean and prepare the attaching s ...
Rear Bumper Impact Bar Replacement
Preliminary Procedure
Remove the rear bumper fascia. Refer to Rear Bumper Fascia Replacement.
Rear Bumper Energy Absorber Nut (Qty: 6)
Caution: Refer to Fastener Caution in the Preface section.
Tighten
40 N·m (30 lb ft)
Rear Bumper Impact Bar
Special Tools and Equipment
...
Installation Procedure
Align the rocker inner panel.
Clean and prepare the attaching surfaces for spot welding.
Apply structural adhesive to all attaching surfaces.
Position the rocker inner panel on the
vehicle.
Verify the fit of the quarter outer panel
Clamp the rocker inner panel into posi ...