Quoted from Chrizg:Leg caster rubber - http://www.pinballlife.com/index.php?p=product&id=564
May want to think about it being by that window. The sun will cause fade.
I use the rubber ones above for the front legs and I put teflon ones like these (http://www.homedepot.com/p/Shepherd-1-3-4-in-ID-Cup-Slide-Glides-4-Pack-9221/202531720) on the back legs.
This way the machine doesn't slide around, but I can still move it by just lifting the front legs.