The models with the black bottoms add a little more contrast making them easier to see when fishing deeper/darker waters. These floats can easily be used for slip float style fishing, are constructed using 1 solid piece of plastic, and are very durable. The Blackbird Phantom Floats come two to a package, have a slit in the bottom section to put the line through, and come with silicon tubing to hold the line in place on the top and bottom of the float.