Nylon cable clamps are commonly used to secure electrical wiring in boats or campers where chafe from constant motion can wear down insulation. Here's an example: https://duckduckgo.com/?q=ancor+marine+nylon+cable+clamps They're cheap, usually sold in packages of 50 for about $5.
Sometimes however, you just need two or three and don't want a pile of clutter, or the store is closed and you want it right away. These clamps print out quickly (six of them print out in 30 minutes on a Lulzbot Mini using Cura's basic normal setting) and are surprisingly strong.
Here's a video comparing Ancor brand nylon clamps (approx 10mm) with ABS and PLA, 10mm and 5mm printed clamps (broken two ways: pulling the loop over the screw, and pulling the loop away from the screw): https://vid.me/YRdm
Spoiler: PLA beat ABS (I hadn't expected that).
Besides the STLs, I've Included the source files. They're in the FreeCAD file format so it is easy to make different sizes or make them better. I think making the larger clamps (10mm+) with a thicker ring wall would make them stronger, but these are good enough for my purposes so I'm quitting here.
Edit: fixed a small error in 10mm files.