more threads or bigger diameter?
 

On Feb 3, 5:22 pm, " wrote:

The load will be subject to intense vibration (its an intercooler
mounted on the front of a car) and weighs about 30lbs.

The oil cooler on the front of our 1989 Ford Mustang GT is held on
with 4 1/4"-20 bolts into some 1/8" thick x 1" wide 5052 aluminum
strips that span the 18" or so from the top of the radiator mounting
bracket to the bottom. The strips are held to the steel radiator
mounting assy with 2 1/8" diameter steel pop rivets at each of the 4
connections. It seems to be holding fine at 165 miles per hour. If
you were wondering, it's a semi-pro racecar, not a street car...