These line holders carry a lot of unique features in a small,light weight package. They are made out of silicone. As a result, the outer rim is designed to flip over your line once on the spool. This helps keep the line secure and adds a layer of protection against dirt and abrasion. The holder also has 2 separate small fly boxes. Not every fly will fit in them. However, as you can see, small nymph and dry flies can easily find a home for a day on the water. We are able to fit up to 20 feet of our floating line on the spool. They also easily fit over most rods.