Measured original 16mm diameter Lego disc.
Designed disc buttons in SketchUp.
Prototyped on MakerBot.
Uploaded to Thingiverse - www.thingiverse.com/thing:1005
Fabricated in plastic via Shapeways.
Fabricated in bronze-infused steel via Shapeways.
Aside: This particular button doesn't fit the Lego piece so looks like the dimensions need to be scaled down a bit to compensate. I'll have to measure the delta when I get home.