What information you will need will depend on who you are ordering them from.
Inland RV and maybe Colin Hyde already know the size, width, etc of the axles that fit your trailer. I understand that they are delivered with no cutting or drilling to get them to fit the mounting plate.
Others, like Dexter, which is where I got my axles from, I needed to know:
Weight rating - Orig. my axles were rated at 4,000 lbs. with 12" brakes, I believe. Dexter had 4,400 rated with 12" brakes. Andy from Inland told me that 4400 is the max rating suggested for my trailer, so I went with that.
Besides that I just needed the measurements that show on the Dexter web site, and the bracket type (top or bottom). You would need the top bracket type, if I'm remembering correctly.
Get the measurements exact (to the 1/16). Mine were delivered exactly as I asked.
With the Dexters I had to do a little cutting and drilling on the mounting plate to get them attached. I'd recommend getting someone to do that for you if you get the Dexters.
Note on measurements: outside hub face is to the outside of the raised area on the hub, where the bolts to in, not the larger flat area of the hub.
As I grow older, I pay less attention to what men say. I just watch what they do.
- Andrew Carnegie