What is a Spindle?
A Spindle is the innermost part of the trailer wheel and axle assembly. It Provides a surface for the Wheel hub (and bearings) to rotate around.
Like most trailer parts, Spindles are an easily forgotten part of your trailer -- until they need to be replaced. So Where are your spindles? What Is a Spindle? What does a spindle do? On today's boat, car hauling, utility, jet-ski trailers etc, the spindles are located at each end of the axles and they definitely do serve a purpose. When you're towing, spindles are the part of the trailer axle assembly that the wheel hubs (and wheels) rotate around. Trailer spindles provide a surface for the inner and outer wheel bearings to roll on -- or rather, to roll around. The inner and outer wheel bearings keep the wheel hub and the spindle from actually contacting one another. In other words, the spindles are literally at the center of it all.
How to find a replacement spindle for my trailer?
Luckily for us bearing manufacturers have stuck to a common numbering scheme. The part numbers for trailer bearings are stamped on each bearing, and are universal. Because these part numbers are uniform, this allows us to determine what spindle you would need based upon simply what bearing numbers you have.
There are generally two bearings in a hub, The front; and the rear. The rear bearing would be the bearing closest to the trailer, the front bearing would be the one closest to the street. Some spindles are tapered, some are straight. What this means is that if you have a tapered spindle, you have a larger rear bearing than front bearing. If you have a straight Spindle, this means that your bearing sizes for the front and rear bearings are exactly the same.
So to determine which spindle you need record the part number for the rear bearing, and the front bearing. Use the following chart to help you determine your spindle specifications: