The one in Bob Boden's possession is five inches.
Huh, bigger than I thought. For reasons of practicality I did mine at ten centimeters, which is about right for a coaster. I also got some 6mm adhesive clear rubber feet to cover up the dots on the bottom and "simulate" the sliders, they work great. (I could put them on top too but why make the top possibly unstable and have someone spill their drink?)
