I recommend you use PETG for its great bed adhesion and mechanical resilience. You could use PLA too, but beware that it will deform over time due to the pressure of whatever you're clamping constantly pushing the arms apart and eventually bending them slightly. If you do choose PLA, you can restore the clip to its original shape by compressing it with some kind of clamp and putting it in warm water for 10 minutes.
If you want to make a custom-legth clip, add imbedded magnets, or change the design enitrely—download the .f3d file.
The author remixed this model.