I purchased new steel hubs for my sprinter for summer tires. The original tires required longer lugs for the aluminum rims. The new hubs need lugs that would match the spare tire. I have six lug bolts that came with the jack etc. for the spare, but I need six more. What is the bolt spec? Where is a good source for purchase. The dealer will not give me the specs, only a set of lug bolts at a ridiculous price.