I recently purchased a Razzi Fidel 9-Tier Filament Storage Rack, but the rack tag design that came with it assumed a multi-color printer and required supports for manual color swaps.   So I designed my own, specifically for the rack I purchased, but should work on any 13mm round pipe. 

It prints in 3 separate pieces.  The clip and holder snap together and the tag slides in with a dovetail holder,.  This allows for the tags to be printed flat and text added in the slicer.    It also requires no supports, printing the clip on its side, and the holder with the bottom on the plate.

I have also designed a tag with a simple 1mm gradient "transparency test", and plan to create other shapes of holders and tags that I will add here in the future.

Print Settings
Layer Height: 0.2mm (0.1mm for transparency test tag)
Infill : 15%
Supports:  None
Materials Tried:  PLA

Although I have not tried it, it should scale to any size round pipe, remembering to also scale the tags and holders to the same size.   😊