A hand wrench or socket ratchet and use some lubricant would be better during the installation to prevent wear and tear. An impact tool or a high speed power driver aren't recommended to tighten the nut. 1/2" diameter x 2-1/16" inside width x 4-3/4" inside length, 2-1/2" thread length,Boat trailer u-bolts are made of high-quality 304 stainless steel（ 2 galvanized mounting plates ），Heavy-duty 304 stainless steel, more robust and durable ,not easily deformed or rusted, more resistant to corrosion and more suitable for marine trailers and motor boats in saltwater, fresh water, coastal conditions and utility/land trailers in icy conditions. Trailer axle U-bolt Kit includes 4 square u-bolts, 2 mounting plates, 8 hex nuts, 8 flat washers, 8 lock washers. U-bolt kit for boat trailer axle leaf springs fits 2" x 2" boat trailer axles with fully adjustable U-bolts to meet your specific needs.ubolt fits perfectly and supports over 150 LBS per bolt. Used to fix or connect locking parts on rectangular wood and metal objects. Suitable for a wide range of applications such as boats, trailers, pontoons, plumbing, and other domestic and industrial applications.