The jack in the trunk has a slot in it and the weight of the car is not on that metal ridge but on flat spots on the side of that metal ridge. When I used my 2 ton jack with the round circle thing - the recessed portions started to bend the frame because the weight was on the thin ridge instead of on the side of the ridge. Confusing as hell to explain... but look at the jack in your car and see hot it fits right at the jack points w/o actually putting any pressure on the ridge? So I have 1 slightly bent jack point too...

 

Sure, but that's a triple seam there, and it's in compression. It's one of the strongest parts of the entire car as long as you don't side load it.

 

OK so this thin seam is ok to put the cup part of a 2ton jack? I have jacked my car up here several times without it screwing with that thin seam. I want to make sure I am not risking something by doing this.

 

Try using a block of wood which should lessen the possiblity of damage to the underbody seams. If only the cup's edge of your jack contacts the vehicle you will most definitely deform the seam. Or you can go to a sporting good store and buy a $2 hockey puck which works wonders for me.

 

Those points should be perfectly fine to use to jack up one side of the car as long as you are careful. if the jack has a cup make sure that no part of the cup sits in those two semicircular cutouts, as it will only concentrate all the weight onto the small amount of area that is resting on the other side of the cup. i use a 3 ton hydro jack with a large flat plate with no damage. of course if all you are using is a floor jack and the car shifts, then thats a different story...