Customiser: hotbed spring washers

Another immensely useful no-brainer: put these around the hotbed springs, keeping those nicely centered, and preventing scratching, shortcircuits, electrolytically induced corrosion and what else may result from allowing the springs to touch bolts or resting surfaces void of protection.
Delivered in a neat package of 9.

For smaller springs, as used with Geeetech G2s, this thing has been reparametrised for 4x6mm springs as http://www.thingiverse.com/thing:1878672