Hex-key size for spur gears in old-style Mach1GTO gearbox


What is the size of the hex-key needed for the set screws on the spur gears in the old-style Mach1 gearbox?  They are smaller than the 0.050" that I have in my hex-key sets.  I do not believe that the spur gears are loose on either axis, but I currently have no way to tighten them if they are.

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