Adjustable Width: The width of this boat guide-on can be easily adjusted, extending to 17 inches at most. It fits any trailer frame less than 3" wide and 4-1/4" tall. Flexible Installation: Our trailer guide-on can be mounted on top of the frame or below it, and the U-bolts fit both large frames and smaller frames. Solid Construction: These square tubes are made of sturdy galvanized steel and are powder-coated, so they work great against saltwater and do not easily rust. With Carpet-padded Boards: The two 45" boards covered with carpet can be fixed firmly onto the tubes, and they will prevent the boat from being scratched. Add the frames effortlessly and keep your boat protected. Wide Application: These trailer boat guides are suitable for ski boats, fishing boats, or sailboat trailers, and they make loading the boat so much easier.