Introduction: Nuts and Bolts: One Fix to Annoying Mixed Unit System. I Made It in TechShop.

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Background 
     When you have a flat tire, you found that the Tire Wrench was unable to take out the bolt that lock the spare tire bracket.  Worse, you don't have another wrench to remove that bolt.  This annoyance would turn to a problem during emergency situation.

Problem:
     Eliminate need for carrying spare wrench just for taking out the bolt locking the spare tire bracket.

Solution:
     Get a 2-inch Hex bolt 3/8" (happen to be the size).  Get an M10 Hex olt (size of  Wheel Nuts.  Use or buy the shortest size to save cost.  Cut off the M10 Hex Bolt Head by hand with a metal hacksaw.  One way is to simply weld the M10 HEX head to the 3/8" Hex head. 
     Another way is to drill hole and insert to the bolt.  I choose this 2nd way.
     Using the drill press to drill 3/8" hole.  Remember to see the speed to low when cutting or drilling steel material.  Insert the M10 Hex Head into the 3/8" bolt.
     One way is to tighten it with the nut. (see picture).  A second way is to use a MIG weld to weld the 2 bolt head together. (see picture). 
     I put the bolt on the vise, inserted the holed M10 Head head, inserted the 3/8" nut and tighten with a wrech really tight.   Then I place the revised bolt with the Tire Wrench on the spare tire bracket.  It worked out very well.

Acknowledgement:
    Thank you to TechShop manager Shawn for giving me a few tips on completing the drilling on the steel Hex head.  Thank you to DC Scott on helping me out as well.

Update:
    I got a photo of the OEM bolt.  Apparently the original 3/8" bolt has an M10 head.  But this bolt would cost $45 to purchase.   The cost of the replacement bolt mod is $4.