Trailer Spindle Sizes: How to Measure and Match Bearings

Trailer Spindle Types: Straight vs. Tapered

Before measuring, it’s important to understand that trailer spindles generally come in two designs:

• Straight Spindles: The diameter of the spindle is the same along its length, so only one measurement is needed.

• Tapered Spindles: The spindle narrows toward the end, which means the inner bearing and outer bearing are different sizes. In this case, you’ll need to take two measurements—one at each bearing location.

Knowing which type of spindle you have will help you measure correctly and match the right bearings and hub.

Method 1: Digital Caliper (Most Accurate)

• Straight Spindle: Place the caliper on the bearing location and record the diameter. Only one measurement is needed since the spindle diameter is uniform.

• Tapered Spindle: Place the caliper at both bearing locations (inner and outer). Record both diameters separately, as they will be different.

On straight spindles, the single diameter equals the bearing ID. On tapered spindles, the larger measurement is the inner bearing ID and the smaller measurement is the outer bearing ID; match each to the chart.

Spindle Diameter to Bearing Size Conversion Chart

Method 2: Tape Measure (Circumference Method)

• Straight Spindle: Wrap the tape measure around the spindle at the bearing seat and record the circumference.

• Tapered Spindle: Wrap the tape measure around both the inner and outer bearing seats. Record two separate measurements.

Method 3: Bearing Part Number (Quickest if Available)

• Remove the bearing(s) from your old hub.

• Straight Spindle: You’ll find one bearing size/part number.

• Tapered Spindle: You’ll find two part numbers, one for the inner bearing and one for the outer bearing.

Use the Industry Part Number Reference Chart to confirm your spindle size.