How to Measure Trailer Spindle Size — EZ Loader & Boat Trailers
Knowing your trailer spindle size is the most important step in choosing the correct hubs, bearings, and seals. Getting this wrong leads to premature wear, leaks, or complete hub failure.
What Is a Trailer Spindle Size?
The spindle is the shaft on your axle where the hub, bearings, and seal ride. Spindle size is determined by the diameter of the bearing surfaces and the seal surface.
---Most Accurate Way to Measure (Recommended)
Use a micrometer or caliper.
- Measure the inner bearing surface
- Measure the outer bearing surface
- Measure the seal surface (rear of spindle)
This is the most accurate method and the only way to be 100% certain of fitment.
---Common Spindle Sizes (Reference)
- 1-1/16" (outer x 1-1/16" (inner) - 5 Lug Hub BT150A
- 1-1/16" (outer) × 1-3/8" (inner) - 5 Lug Hub H1000
- 1-1/4" (outer) × 1-3/4" (inner) - 6 Lug Hub #535
These are typical sizes used on many EZ Loader trailers, but variations exist depending on axle rating and year.
---Can You Measure with a Tape Measure?
Yes—but only as an estimate.
- A tape measure or ruler will get you close
- Measurements are usually taken to the nearest 1/16"
- This method is not precise enough for ordering parts without confirmation
Many aftermarket bearings are manufactured using metric tolerances, even when labeled in standard inch sizes. This is why precise measurement matters.
---How to Identify the Correct Seal Size
Measure the seal surface at the rear of the spindle where the grease or oil seal rides.
EZ Loader trailers commonly use oil bath hubs, which require a double-lip seal designed to keep oil in and water out.
This seal functions similarly to a crankshaft seal in an engine—if it leaks, the system fails.
---Common Mistakes When Measuring
- Measuring worn or damaged spindle surfaces
- Confusing inner and outer bearing sizes
- Assuming all EZ Loader trailers use the same hub size
- Ordering parts based on guesswork instead of measurement
Not Sure What You Have?
Call 843-784-5797 before ordering.
Have this ready:
- Trailer model (if known)
- Photos of your hub or spindle
- Any measurements you’ve taken
We’ll help you match the correct hub, bearings, and seal the first time.