Hi I think the reason they use that funnny bolt (not an allen key nor a torx bolt is so that you don't start doing the brakes and then suddenly find the caliper applies the handbrake electronically to the rear wheels. I know Mercedes, and VW and some Fords have gone that way but I don't have access right now to check that information for you. Who would have thought thirty years ago you would need scan tool to retract brake calipers or work on brakes. Alldata is the best source for that information.