Customiser: hotbed spring washers for G2

Parameters of http://www.thingiverse.com/thing:1804488 changed to fit the smaller springs of the G2s Delta printer (outer spring diameter 6mm, inner 4mm, M3 screws), with narrower wall and thinner base. Code remains unchanged.
Still 9 in a set. Pick the 6 nicest, use the remaining washers as 3-point coasters.