heli-coils in rear hub carrier

["Walter" <Whalt@xxxx>]

In the process of replacing my rear brakes (I finally made some time to work
on it today, yeaaa!) I noticed that the bolt holes in the rear hub carrier
that hold the brake calipers on had heli-coil inserts in them. My immediate
thought was that some previous mechanic stripped the threads and did a
marginal repair to a critical part. Well, I compared to another DeLorean
and looked in the parts manual, and evidently this is the way they are
supposed to be. But to me it makes no sense why they used a heli-coil when
a regular thread might do better. Can anyone say if all the hub carriers
were originally tapped with the wrong size and had to be fixed with a
helicoil? Or did they use the helicoil to make the aluminum threads
stronger? It seems this would make it weaker, but I'm not a metallurgist.
It also seems strange that they would use a 7/16" x 20tpi bolt with a 5/8"
head when they could have used something in metric. After all, the front
calipers are held on with metric bolts, so why were the rears done in
odd-ball inch stuff?

Walt Tampa, FL