go kart wheel mounts

evening all
i have a set of rear wet weather go kart wheels that i am struggling to figure out what size mounting hubs to use and i cant get my calipers in to measure them cause of the shape of them i was wondering what other people have done to figure out the size and if anyone has any recommendations on what hubs to get that would be great

im planning to run these off a chain drive from 1kw scooter motors

thanks guys

Put some threaded rod in the bolt holes longer than the width of the hub and measure the distance between them using your calipers.