PO-20 Symbol buttons for Pocket Operator case

Buttons engraved with PO-20 model symbols. Compatible with the Pocket Operator case: http://www.thingiverse.com/thing:1375818

* The "v4" version are the same buttons as included with the Pocket Operator case. The details of the symbols will need a very small extruder when using FDM. Extrusion diameter of 0.3 mm or smaller recommended.

* The "v4wide" version of the buttons has a larger diameter (0.5 mm), less fillet and slightly larger symbols. These are intended to be used when the both ca