3/8th SAE socket organizer, This isn't a rail it is a modular system. print end caps, print the number of standard holders to match your set and spacers if you need them for larger diameter sockets. These have embedded neodymium magnets, universal fit (attachment point to the holder is the drive socket) and, fully expandable to match your set. 

The files here have four plates with pauses built in for magnet insertion. the first three are the endcaps and standard holders, these all use the same magnets so you can add them to a single tray and print what you need. The magnets I used are these from amazon (40Pcs Rare Earth Magnets Bars, Rectangular Metal Small Neodymium Magnets, for Cabinets Refrigerator Cruise Crafts Industrial Kitchen Tool Storage (20x10x3mm): Amazon.com: Industrial & Scientific) the hold is OK despite the size sold as I measured these and the cavity modeled is to my measurements. (19x9.1x2.6). If you want more hold add a negative at the same level as mine and size it to the magnet you have. For the spacers they are too narrow for this magnet I have a standard disc magnet in these 8x3. 

All pieces are double dovetail connections so you can build as many of these as you want and simply add more as your socket collection grows. The colors shown are my stand color for SAE but are separate filaments in the slicer so you can make them whatever you like. 

Absolutely looking for feedback if you like them, don't like them think I should change or improve something please let me know.