Adafruit Ball Caster - 3/4" Metal Ball [ADA1200]
Get your robot rolling with this durable and smooth metal ball caster. We like the size (not too big, not too small) and surprisingly smooth motion of this caster. It's also really easy to attach, with two screw mounts (and included screws) that will allow you to attach it to any material up to 5mm thick.
Ball Caster - 3/4" Metal Ball