This trailer axle U-Bolt Kit is designed to be used with a 1 3/4" round axles. The leaf spring u-bolt kit includes four raw steel 3/8" diameter u bolts that are 1 3/4" wide inside and 4 1/4" long. Also included in this kit are two mounting plates and eight nuts. This kit is most commonly used on smaller utility and boat trailers. The 1 3/4" diameter trailer axle would typically be a 1400 lb to 2,000 lb capacity trailer axle.