This is a protective case for a very tiny USB <-> UART converter found on ebay.
If the link doesn't work search for CP2102 Micro-USB UART.

The diameter of the holes are 1.8mm. Due to little shrinking you can stick some transparent filament (1.75mm) into the holes as a light guide for the LEDs. I still had to use a 1.6mm drill to widen the holes, so the filament can be press fitted.

For the full top cover version I've used "toner transfer" method to label the pins.
If you use PLA, forget it :)

Update 2016-03-27 22:38 UTC:

• added full top cover as alternative

Update 2016-03-27 14:41 UTC:

• slightly repositioned the holes for RX & TX LED

Zortrax M200

Doesn't Matter

No

90 micron