Which size Allen key do I need for my Ground Control?

 

4.5mm. Good luck finding one, I have one in my Crafstman set, which I forgot to bring to the track one weekend. The only thing I could find at the parts stores / hardware stores that were nearby were either 4 or 5s.

 

I know this is old as dirt but i found that a t30 torx bit fits perfectly. thats on my 99 civic so hopefully its the same for all hope this helps someone.

 

silly, but in a pinch you can grind down a flathead screwdriver a little at a time to fit. NOT a good suggestion but if you really needed to....
hell i made a crank key our of an allen wrench along side of the highway cutting it with a set of vice grips that had the cutter in tha back of the jaw... not a good fix, but it got me to the nearest honda dealer to get the proper key