So I just got under my car tonight...
I already made my ends (1.5" diameter round bar X 1.5" tall) today, and I just picked a 1.5" hole saw to fish mouth the ends on the 1.5" diameter steel tubing.
The sizes I have under my car are as follows:
10mm bolt hole in the brace that is welded to the twist beam
**ASSUMED** 15mm hole in the twist beam
821mm spacing between bolt hole centers
^^^^^^^^^
The 821mm bolt hole spacing is (in my eyes) a fluctuating number. I believe the actual size should be 820mm. But since the braces are welded on, the bolt hole centers may shift from car to car....
I am going to be drilling out these holes to 5/8" so that they will allow for a little wiggle room for alignment with the (presumed) 15mm holes above them. I realize that this would make the hole 15.875 mm, and the fasteners i am using are 14mm, resulting in an overly sloppy fitment. I would prefer to keep bolt holes 1mm larger the fasteners typically (or 1/16th larger in imperial sized fasteners), but I want to make sure all the bolt holes line up in the end.
Oh and the flat section located around the 10mm bolt hole is in fact 1.5" in diameter, so try not to go over that size for your mounting points.
Sorry this took so long for me to get up on here. Busy BUSY weekend.