3D-Printed Screw-In Front Lenscaps

Here's a really quick and easy 3D-printable screw-in front lenscap design, set-up as a customizer application. __Less than $0.15 worth of materials__ are used to make a typical size lenscap, yet they work well and can even __double as color references__.
An Instructable gives the details: http://www.instructables.com/id/3D-Printed-Screw-In-Front-Lenscaps/

Note: An improved version of this is now available as http://www.thingiverse.com/thing:1563812