If you own a trailer, at some point it may be necessary to measure the hubs in order to replace a wheel or a hub. Hub bolt patterns are described by the number of bolts per wheel and the diameter of the circle that the bolts are arranged on, so it will be necessary for you to take accurate measurements. A typical designation would be 5 on 4-1/2, which would mean 5 bolts spaced evenly on a 4-1/2" circle.
Count the number of lug bolts on one wheel. Trailer hubs typically have 4 or 5 bolts per wheel, but heavy-duty or homemade trailers may have 6 or even 8 bolts per wheel.
If the trailer hubs have an even number of bolts holding the wheel, measure from the center of one bolt to the center of the bolt directly opposite using a tape measure or calipers. If the bearing cover in the center of the wheel is in the way, you can remove the wheel and measure the distance between the centers of the opposite mounting holes on the wheel itself. The hub bolt pattern will be determined by the number of bolts and the distance between the opposing hub bolt (or wheel hole) centers.
If the hubs have 5 bolts, the process is slightly more complex. Choose any bolt to begin, and measure the distance to the center of a bolt on the opposite side, being sure to skip one bolt going in either a clockwise or counterclockwise direction. Multiply your measurement by 1.0515, and the resulting number will give you the diameter of the bolt circle.
