This is a spool filament clip. It prints quickly, uses only about 1 gram of filament (0.33 metres of 1.75 mm filament), and is very easy to use.
It clips onto the spool of any brand of filament, so it's a universal clip. It can clip onto 1.75 mm filament or 2.85 mm filament, so it's a dual-filament clip. It's shaped like a dragon, so it's a dragon clip. Hence the name Universal Dual-Filament Dragon Clip.
The easiest way to use it is to snap the filament in from the back of the head to secure it and slide the filament out from the side to release it.
There are 4 variations of the clip:
UniversalDualFilamentDragonClip.stl - 4.2 mm thin
UniversalDualFilamentDragonClip-thick.stl - 6.35 mm thick
UniversalDualFilamentDragonClip-NoSpikes.stl - 4.2 mm thin, no spikes on back
UniversalDualFilamentDragonClip-thick-NoSpikes.stl - 6.35 mm thick, no spikes on back
Why another filament clip.
I've always used filament clips that clip to the filament itself, but I was curious to try one that clips to the spool, so I searched Thingiverse for the best one. I found one that I determined was probably the best design, but it has errors when loaded into the slicer and it has unwanted branding on it. So I removed the errors with netfabb basic and then removed the branding with Blender.
Since the original seemed unnecessarily large, I created another version where I reduced the thickness by a third by scaling the Z dimension from 6.35 mm to 4.2 mm. The thinner clip seems to work just as well as the original-sized clip. I included the original-sized clip as well since neslekkim pointed out that the thinner ones get a bit stuck in the honeycomb sides of Prusament spools. I also made versions with no spikes on the back that you might want to use if you store your spools in plastic zip-lock bags inside the original boxes since the spikes could puncture through the bags.
Credit to Original Designer
This is just a simple remix of Khaleesi Clip Dual Sized Filament Clip 1.75 & 2.85mm by sneaks and all credit for this excellent design goes to sneaks; I've done nothing other than remove the errors and the branding and the spikes and scaled it in the Z dimension.