soooo. I just spent 1.5 hours changing the shims in my front diff...........I will never change diff fluid at the track, this is kinda retarded. With practice I am sure I would get faster and with a power screw driver even faster. But wowzers. Anyway. The .5mm seemed to fit fine. But truth be told the original shims seemed pretty tight. No metal in my diff and near excessive wear that I could see. The .5mm shim fit fine. Maybe a tad tight. I think .4mm is probably the sweet spot. but the .5mm went in easy mode. No binding that I could see and the front wheels spun free without the belt attached. I am not motivated to do the rear diff tonight, I will do it when I change the diff fluid, lol.