I don't know. But I suspect that large nut you see is actually a grease cap.
Use a large pipe wrench (Stilson wrench) and turn the "nut" counter-clockwise. If the nut just spins in the hub and doesn't screw out, then it's a pressed-in grease cap and not a threaded cap.
Grumpy ole man with over 50 years towing experience. Now my heaviest trailer is a 7,000-pound enclosed cargo trailer, RV is a 5,600 pound Skyline Nomad Joey 196S, and my tow vehicle is a 2012 F-150 EcoBoost SuperCrew.