After seeing hundreds of broken center pins on the Rubicon Trail, we don’t sell any u-bolts smaller than 5/8” thick! Our u-bolts are zinc plated and built from 5/8” material with rolled threads. All u-bolt dimensions are measured from the inside of the bend to the top of threads. The width is the inside measurement, or more simply, the size of the tube it will slip over. All u-bolts and kits come with tall nuts and washers.