Got a boat trailer & the rims are a bit worst for wear :(
I want to get new 1's, but how do I figure what stud pattern/axle they are? Use to be able to look on the inside, but to much rust to see anything, all I can tell you is they're 5 stud 13's

TYI :)

Measure the distance between the studs... 116.3mm or 100mm, determine how big the spigot hole is, and offset (negative, positive, and by what amount)... Some trailers have a Ford hub, some have completely different ones, hopefully you'll have a Ford one, then you can stick some E/X series rims on it. Otherwise I guess a tyre place should be able to tell for you

most older trailers are holden or ford stud pattern. try ur spare wheel on it and if it fits but the bore is bigger then its ford. if the studs are too wide its holden.