Original Whale Tail XL Aluminum Stabilizer and ski fin. The Whale Tail XL looks different because it is different. The unique Whale Tail XL design extends out behind the prop to utalize the prop wash energy that normally is lost breaking the water. It transforms that energy to lift against the Whale tail XL for immediate response when the throttle is applied. All the other brands are a poor quality "knock off" of this one. All other brands work off of forward motion only which make them only half as effective as this one. Stainless mounting hardware included. 15-1/2" wide X 13-1/2" long. Works on all I/O's and outboards. Increases top speed in most applications. 3/16" strong marine grade aluminum. Durable anodized finish. Stabilizes bow-light boats. Reduces porpoising and cavatating. Smooths out ride in rough water. Flattens wake for water-skiing and creates positive skid free turns. Pops up skiers in less time. LIFETIME WARRANTY. This is an actual emailed testimonial from one of my customers: (first email) Payment sent! Honestly, I have several motors, and five of them have various other types of what everybody calls "whale tails". Let's redefine the terminology and call them something else. Maybe "stabilizers". It's like they don't even exist compared to the REAL Whale Tail XL. That's why I'm ordering more. Much quicker out of the hole, especially with skiers. Much sweeter trim out. Much higher top end. I'm just chunking my old style as I replace with the XL. Sincerely, Allen Clark (second email) If you want to use my comments as a testimonial, please feel free to do so. I HAVE WITNESSES TO THE FACT OF THE HIGH PERFORMANCE! Allen Clark