The below are American Gold Eagle 1 oz bullion coins. All the precious metals images are apparently from the Public Domain.
Below is a Gold Eagle, a Silver Eagle and a Platinum Eagle
Below are pictures of bearings!
Bearings from China -- alibaba.com
^----- a tapered roller bearing, used in wheels of cars.
Copied from wikipedia, an animation of dirt in a ball bearing, look carefully to see the red spot (dirt) on ONE of the steel balls --->