Rear fender mounts with (x3) 2x4mm screws. I updated the piece for more support where the screw holes are. The basic white might come with some "stepping" surface marks from the process Shapeways uses to make these, but the colored ones look really good ( I have seen Black and Purple). The colored surface is matte in finish.
To screw the piece in, I recommend screwing in the front post halfway and then the side ones halfway. Once all screws are in place, finish tightening.