[tsubaki]

From what I remember there are several manufacturers of that type of spindle/grease situation. I've got two trailers that have that setup.
Seemed like there is a decal and sticker on the trailers that identified the spindle/bearing situation. And "might" have the size or part number affixed for identification.
The trailer load rating might give some insight as to the bearing size.
The hub pattern can be determined by measuring from the center of the hub to the center of one of the lug bolts and then multiply by 2.