You are correct that these two hub and drums are exactly the same but one has a standard grease cap and the other has an E-Z Lube grease cap for E-Z Lube spindles, so both will fit 12" to 15" wheels. The correct one for you will simply depend on if you have an E-Z Lube axle or not:
- Dexter Trailer Hub and Drum Assembly for 2,000 lb E-Z Lube Axles # 8-257-5UC3-EZ
- Dexter Trailer Hub and Drum Assembly for 2,000 lb Axles # 8-257-5UC3 view full answer...