Silly Putty® Wheel Mask -- A Quick How-To by ChillyB
I don't know whether this has ever come up before in your modeling lives, but I found a need to mask the center of a wheel painted one color while painting the rest of the wheel another color. This is what I came up with:
Using a drafting template, I first select a suitably sized circle:
Next, I use a small ball of Silly Putty® to fill in the circle equal to the thickness of the template:
Finally, apply that circle of Silly Putty® to the wheel, taking some care not to distort it too much in the process:
This is how they turned out last time I tried this:

Source: http://cs.scaleautomag.com/SCACS/forums/thread/995377.aspx
Lorenzo Bandini Henry Banks Fabrizio Barbazza John Barber Skip Barber