These center caps are designed to fit Generation II Prius (2004-2009) 15 inch wheels. These are based on precise measurements of Toyota part #42603-52030.
This has the iconic power symbol embossed in the top of the wheel cover, just like the power button in your Prius. More info: en.wikipedia.org/wiki/Power_symbol
Also fits Yaris, Vios
Nylon is NOT UV stable. For maximum longevity and downright good looks, you will want to paint this object. Acrylic paints with a glossy topcoat are a proven method of painting objects printed using Selective Laser Sintering.
Shapeways has a tutorial here: http://www.shapeways.com/tutorials/painting3dprintedsls
And a blog entry here: http://www.shapeways.com/blog/archives/129-painting-your-3d-printed-models.html
Further, you can locate the recommended Tamiya paints here:
THIS DESIGN HAS NOT BEEN CONFIRMED TO FIT GEN II PRIUS WHEELS UNTIL THIS DISCLAIMER IS REMOVED.