I would suspect that it varies depending on year, and model. Someone have a master list of these? I can say that 2003 2500HD uses a T55 torx Take it to the local autoparts store, ask them to help you pick the right one - they will usually let you go out and try them out for fit. -KS
18mm
3/8 inch allen.
3/8"
Bolt pattern for a 1985 GMC Sierra Classic 1500 is 6x5.5 (That is what mine is)
should be 6 x 5.5
GMC has three different bolt patterns: The Acadia has a 6X132 the Envoy has 6X135 and the full size such as Yukon and Sierra which have 6X139. Hope this helps you.
12mm bolt on the rear. Like a 16mm nut style head on the slider. Hold the head of the pin to break the bolt loose.
6x137.5
6x5.5
8x6.5
6x5.5
5x5