Mcgard part# for wheel locks for the 19" wheels with the wheel nut cover center cap is:
Under Hub Cap Lock part#24019
Thread size:M14 x 1.5
OEM Hex Size:22mm
Unfortunately GM dealerships cannot supply OEM locks for the 19" wheels in my area.
Sorry for the late reply, but if you have the factory 19" on your 2011 the wheels and locks are the same as my 2009 the nuts are the ones that go under your wheelnut cap, wheel nuts and stems are the same thread and size hope this helps good luck! :thumb: