Strut mount with bearing and insulator - bearing function

[hjb981]

I am about to change my front struts and strut mounts, and after just receiving the parts I am a bit confused about how the strut mount bearing is supposed to work. The strut mount (including bearing and insulator) is AC Delco, and it consists of a big metal plate with three screws and a central hole with a rubber bushing, which is where the top of the strut will go. Then there is a large, rather hard "rubber ring" that I guess is the insulator. The shape is like a doughnut that would have a square cross section. In this insulator, there is a square "grove", or cutout, from its inner-diameter part on one side, and the thing which I suppose is the bearing fits in that groove. The bearing is a part that has white plastic on one side, and rubber on the other, with some grease in between to make it turn easier. When this part is inserted in the cutout of the insulator, with the plastic going into the insulator, the rubber part makes contact with the insulator, preventing it from turning. It looks the same on both strut mounts. I guess I am missing something... If anyone could explain it, I would be grateful.