Metric vs Unified threads

[CrashBob]

Guys,
Got a little issue that came up when trying to install my new wheels. The nuts are Metric and the studs are 1/2-20 UNF. Use the old nuts? No can do, the nuts for the new wheels are threaded on the outside to hold the nut covers which hold the center cover on.
I have thought of a couple of solutions: Drill and tap for helicoils or get metric studs and replace my old ones. The second fix sounds like a bunch of work and cost.
I will check the hardness of the nuts for machinability at work tomorrow and probably visit with one of the materials engineers to see if the helicoil idea is valid.
In the meantime, anybody have any similar experience or a "magic" fix?

Thanks,

Crashbob