If you own a boat, you can most likely use cup holders. One of the worst things about boating is that most boats do not come with cup holders. Online stores can charge more than $150. I have even seen some for more than $250, and that's an insanely inflated price.
Many people want a chrome cup holder for their boat, but that's generally not the best. A stainless steel cup holder looks the same as a chrome one, but it will not rust. Stainless steel holders also last much longer and are really sturdy. In the event you have chrome on your boat, you will know that it is very easy to get rust. It can be very difficult to get the rust out of the chrome, and a much bigger pain.
The stainless steel bracket bolts directly to the boat railing. It comes with a couple of stainless steel screws that secure the bracket to the railing. The bracket that connects to the railing is adjustable, so you can position the holder any way you want.
A polished stainless steel cup holder is far superior to one that is made of plastic. Plastic cup holders get scratched very easily. They also tend to break very easily. Not to mention that they change hue due to fading from the sun. Generally, it is a pretty bad idea to purchase a plastic cup holder as they basically do not last long.