Karl,
Saving the threads, even if it were possible is a waste of time, because the
treads have become aluminum oxide and have no residual strength anyway. Next
time use anti-sieze at assembly. Most likely the fault was electrolysis, as
they were probably diecast and zinc is often alloyed with the aluminum to
promote flow in the mold. In the presence of water, the unit becomes
thousands of little batteries.
Steve

"Karl Townsend" wrote in message
anews.com...
My son just gave me a little job... I've got six aluminum pickup topper
clamps that used steel bolts. They are all corroded together. if you just
twist hard, the bolt will take the AL thread with it.

Short of cutting the bolt off, milling and tapping to the next size; how
would you repair this?

Karl