In order to replace a hub on your trailer, you will need to know the bolt pattern or lug pattern. Trailer wheel hub patterns can be defined by the number of bolts or lugs per wheel and the diameter of the circle that the bolts are arranged on.  Determining the bolt pattern is rather easy, but it is very important that accurate measurements are taken.  The majority of boat trailers on the road have a 4, 5 or 6 lug pattern. A very common designation for trailer hubs would be 5 on 4-1/2 or 545 for short.  This means that the hub has 5 bolts spaced evenly on a 4-1/2″ circle (see 5-lug diagram).

Determining the bolt pattern on your trailer:

1. You will need to first count the number of lug bolts on one wheel. Most trailer hubs typically have 4 or 5 lugs per wheel/hub. Heavier duty, higher capacity trailers generally have 6 or 8 Lugs per wheel.
2. 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 ruler, tape measure or caliper.  The hub lug bolt pattern will be determined by the number of lug bolts and the distance between the opposing hub bolt (see 4-lug hub diagram).  All but 5-lug patterns are measured in this manner.
3. If your trailer wheel hubs have 5 lug bolts, measuring is slightly different. Choose any lug bolt and measure the distance between the back of one lug to the center of another that is directly across from it. Be sure that you skip one bolt when measuring.  You can measure the distance in either direction

The two most common lug patterns are 4 on 4″ and  5 on 4-1/2″ hubs. These hubs are typically seen on smaller trailers.

NOTE:  If you are replacing older wheel hubs, wheels, integrated hub/drums or hub/rotors the bearings should be checked for wear and replaced as necessary. Always use a high-temperature wheel bearing grease when re-packing your trailers hubs.

4, 6 and 8 Lug trailer wheel hubs are all measured in the same manner.