Knowing your trailer axle size is important when ordering brakes, hubs, bearings, seals, suspension parts, or replacement axles. The good news is there are several ways to identify it.
1. Check the Axle Tag (Best Method)
Most trailer axles have an identification tag or sticker attached to the axle tube.
Look for:
- Capacity rating (ex: 3,500 lb, 5,200 lb, 7,000 lb, 10K, etc.)
- Axle serial number
- Part number
- Manufacturer name
Common locations include:
- Center of the axle tube
- Behind the hub
- On the axle beam
Manufacturers like Dexter, Lippert, and Rockwell often include model information directly on the tag.
If the tag is readable, this is usually the fastest and most accurate method.
2. Measure the Axle Tube Diameter
Axle tube diameter often gives a good clue to axle capacity.
Here are common trailer axle tube sizes:
| Approximate Tube Diameter | Common Axle Capacity |
|---|---|
| 1.75" | 2,000 lb |
| 2⅜" | 3,500 lb |
| 3" | 5,200–7,000 lb |
| 4" | 8,000–10,000 lb |
Important: Tube size alone is not a guarantee since some manufacturers vary.
3. Identify the Hub Bolt Pattern
Wheel bolt pattern can also help narrow it down.
Examples:
- 5 lug → Often 2K–3.5K axles
- 6 lug → Common on 5.2K–6K axles
- 8 lug → Common on 7K–10K axles
Again, this only helps estimate capacity—not confirm it.
4. Pull a Bearing Number
One of the most accurate ways to identify axle size is by checking the bearing numbers.
Remove the hub and look for numbers stamped on the bearings.
Examples:
- L68149 / L44649 → Often 3.5K axle
- 25580 / 14125A → Common on 5.2K–7K axles
- 387A / 25580 → Often heavier axles
Bearing combinations help determine:
- Axle capacity
- Hub compatibility
- Seal size
- Brake fitment
5. Measure Hub Face & Spring Center
If replacing the whole axle, you’ll also need:
Hub Face Measurement
Measure from outside wheel mounting surface to outside wheel mounting surface.
Spring Center Measurement
Measure from center of spring seat to center of spring seat.
These measurements are critical when ordering a replacement axle.
6. Check Brake Size
Brake dimensions often indicate axle size:
- 10" x 2¼" brakes → Often 3.5K axles
- 12" x 2" brakes → Common on 5.2K–7K axles
- 12¼" x 3⅜" brakes → Often 8K+ axles
Still Not Sure?
If the tag is missing, don’t worry.
Take a few photos of:
- Axle tube
- Hub face
- Brake assembly
- Bearings (if possible)
Along with:
- Bolt pattern
- Tube diameter
- Trailer GVWR
These details can usually help identify your axle quickly.
The More Information, the Better
Ordering trailer parts based on guesswork can lead to the wrong bearings, seals, brakes, or hubs.
A few measurements now can save a lot of frustration later.
At Highway Trailer Company, we help customers identify trailer axle sizes every day. If you’re unsure what axle you have, send us photos or measurements and we’ll help match the right parts for your trailer.