There are a few measurements that you need to be aware of regarding
boat trailers. To get the measurement it's easiest if you remove
your tires and wheels. It's also helpful to have a friend hold one
side of the tape measure but not absolutely necessary. To obtain
the hub face measurement, first hook your tape measure to outside art of hub, that is the part of the hub that is facing the wheel.
Measure across the axle to the exact same spot on the opposite
side. Be careful not to measure to the inside of the hub, only the
outside. This is the primary measurement that is needed. The rest
of the measurements below are alternative measurements that can be
used to arrive at this measurement.