It measures 2"o.d., 5/8" i.d. by 1/4" in thicknesses, when in place it compresses both the lower and the upper rubber mounts by that 1/4", I'm guessing that in doing so it's twisting the diff clockwise ever so slightly when viewed from the rear, hence the effect on the ride height. I had it fitted for around a month and it hasn't done the Polybush mountings any good at all, I would like to replace them again. It was suggested that perhaps the mystery washer would counteract any effects of torque on the diff but I am honestly no wiser. However, there MUST be a happy medium with the assembly detail in the workshop manuals stating that the lower rubber mounting washer must be free to rotate when everything is tightened up. Too free and you've got a sloppy mounting, too tight: are you affecting alignment?