Inside the kegerator/keezer all the lines look the same. This snap-on cover helps differentiate which lines run to which tap. I prefer L=Left and R=Right, for my 2-tap kegerator, but 1-n is also a great idea for multi-tap keezers. These can also snap on the gas connects to mark different pressures, e.g. Lines set to Serving pressure versus Carbing pressure.
Caps print top-side down, so supports are not needed.
I included STLs of the options I like, but use Customizer to label your lines as you like, you can even use longer text if you don't mind the appearance.
And remember... RDWHAHB
UPDATE: 22 September 2018
I reprinted a part on my Prusa, and realized the old M3D printer had terrible tolerances.(especially for circular items) I updated the included STLs to be 0.5mm tighter, and kept the old one's with "looser" added to the name. The new version exposes this to Customizer as
ExtraMargin Setting extra margin to 0.5 is equivalent to the original version. Default is 0
Original prints (and photo) were made on M3D Pro