Why are frame mount holes so large?

'76 and up frame, why are their two holes? A smaller one and the larger one? And why is the larger one so large?



Current plan is to make mounting plates that bolt to both holes, with 1/8" rubber between the plates and the mounts. Large bolt is 5/8" grade 5 and smaller is 1/2" grade 8.

I and make 1" or so rubber bushings to put below the mounts like the original mounts. But what is the purpose? Adjust the tub so it aligns? Why does the tub not shift slightly with such a large hole? Do I need to make another bushing that fits the ID of the hole and the OD of the bolt? A washer to hold it in place?

Sorry for so many questions but this does not make since to me.

 

I thought 76+ have sleeves/bushings inside the rubber that the bolts slide through. Don't you want them big for some flex?

 

the factory rubber fits through the hole with a corresponding rubber that fits over that one and flat to the bottom side of the mount

 

There should be a corresponding hole in the body, used for body/frame alignment purposes which is why the holes are so large.

 

Body bushing should have a shoulder that goes through that hole that allows for side to side flex.