On a 1992 Chevy lumina van there are Allen head bolts holding on the brake calipers what size wrench do you need to remove those bolts?

The size of the Allen (hex) head bolts on a 1992 Chevy Lumina van's brake calipers is most likely 7/16 inch or 11mm. However, there's no guarantee without visually inspecting the bolts themselves. It's best to have both sizes of Allen wrenches (or sockets) handy. A mechanic's tool set will typically include both.