We at Rockin Frames value style. We also love music, and our company name is a play on both rock music and rocker. We appreciate metal, too. As we were designing our bearings we got the idea to somehow show that appreciation, and came up with our Black Metal Bearings. Naturally, they have a black finish. The Black Metal Bearings are RS, which means they are rubber sealed on one side and the other side is open. The black rubber shield is not only stylish, it protects the front of the bearing from sand and dust and helps to prevent water from getting in. Our bearings are serviceable and that means, among other things, sustainable. When they do need maintenance it is very easy to do.