The little gold dome things are "spring retainers" that keep the shims in position on the caliper piston internal diameter. The front caliper pistons have an internal diameter that is similar in size but the rears are not interchangeable. One of the pistons is smaller and require a different part number. I had to re-use the smaller ones on my 2001S. They had enough stick to use again. The sticky surface helps the pads release from brake disc when caliper pressure is let off. Used Wurth spray on installation on pad backing plate. Nice and quiet with no problems. Good luck and enjoy your car.
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