The Bullnose Rudder measures, 10.5" high x 4.75" wide, and fits on a 1 1/8" (1.125") shaft diameter which is a common size for "MOST" 24-55lb shafts. It is designed to give you better control of your watercraft in most windy conditions, help hold a true course at most trolling speeds, and prevent the boat from spinning as much when the motor is off. Please note, it will NOT work on a self deploy bow mount trolling motor. It's most commonly used for "but not limited to" minnkota trolling motor, motorguide trolling motor, newport vessel trolling motor, trolling motor for canoe, etc... Common tiny boats used are, inflatable pontoon, Pelican Bass Raider 10E, fishing kayak, canoe, jon boat, Ultraskiff 360, just to name a few. If the shaft is too slim, no worries, there is double sided foam tape provided in the packaging to shim a thin shaft. It also has a unique design shape to accommodate your prop. If there is minimal clearance between the shaft and the prop, simply flip it upside down. It will perform just the same while allowing the prop to spin freely without any interference.