I originally posted this method on MyLargeScale possibly 15 years ago. That post and the photos are long gone 
I needed to paint a bunch today - so I took pictures to put the method back out there again. I am using Aristo chrome finish metal wheels, but this method would work for any brand / color.
I start with a bunch of rubber O-Rings that are sized to match the tread diameter of my wheels. The O-Rings are about 1.375" outside diameter. They slip over the tread masking it and the flange from paint. Next I mask the axle ends with some wire insulation that has been plugged at one end with a short piece of solid wire - #14 I think…
The trucks were painted previously using the same paint colors / technique. I made up a jig to hold the wheels while I paint the axles and the back…
I am using Krylon Ruddy Brown Primer as the base color, then misting with Krylon Flat Black before the ruddy brown dries. Here the Rudddy Brown has been sprayed on the backs and the axle. Paint on the wheel faces is just over spray…
The wheels are taken out of the jig to paint the faces. In retrospect the jig was probably not needed at all…
Next, the wheels are misted with the Flat Black to darken up the color getting closer to an old rust color…
Back indoors an hour later the o-rings and insulation masking is removed. One pair has been installed in a truck. I lubricate the axle ends with Hob-E-lube oil…
These wheels and trucks were prepared to finish the Delton Wood Hoppers I picked up last weekend in York…
Before coming up with this method I used to paint everything then clean the axle ends and treads with lacquer thinner. This is much faster and lots less exposure to nasty fumes!
