JMauld: If it takes the size down to .5", then you could use a 1/2 inch bolt. I think it would fit through the axle, but maybe not? My engineering cheat sheet shows a clearance hole for a 12mm bolt to be 13mm (so the hole through the axle should be 13mm - .5118").
The VW rear axle is a U shape with the bottom of the U at the mounting point. This setup gives a different style of single wheel compression. So, each wheel is connected to a "leg" that is allowed to flex up. A downside to that setup is that the two wheels are not really connected to each other across the car (to help split the cornering loads). Almost like independant rear suspension. But, there is no panhard bar because the axle is more like a trailing arm in design....sorta
The Mitsu stuff uses a U shape where the wheels are attached to each other and the legs of the U are mounted to the frame. Because the wheels are together, if one wheel wants to be compressed, then they both must tilt (think camber tilting). In order for this to happen, the mounting points must be flexible enough to allow this tilt. (ie thin plate type material that mounts the axle). When those mounts are that flimsy, then the cornering loads would push the axle right out from under the car. Thus, panhard bars. They mount to the frame and locate the axle horizontally under the car. This setup also has a downfall, as the axle moves throughout it's compression, the axle must also move side to side (calculated by the arc movement of the panhard bar as the radius). This also means that the entire cornering force is transferred through the panhard bar into the chassis. ie, a really good reason to beef them up. This is also the reason for reinforcing of the panhard mount at the chassis side. I have personally seen that mount torn off the chassis. I run a second hard mounted bar from the bolt that holds the panhard to the chassis back across the car to the other frame rail. That bar doesnt move, it is part of the chassis.
http://www.geocities.com/colt4rally/old ... upport.jpg
BTW, I did taco a panhard bar rallying last year.