Update 01.01.2019:

After some time using this design, I felt that it needs a means of making the spools turn more evenly and easier. Especially with cardboard spools. I don't like the ball bearing designs for their inherent danger of unwinding too much and hence causing filament entanglement. I have some teflon cable wrap lying around with exactly the properties I need for this. Also the tip of the latch seems a little bit too pointy to be safe.
So this is my updated version with a pocket for some teflon wrap and a rounded tip on the locking latch. I am thinking about making a version which will use two pieces of teflon bowden tube instead of the teflon wrap. People who have a 3D printer are more likely to have that lying around than the teflon wrap right? Please give me a short feedbak if you want this design. Also I'd like to know how people get along printing this little "warpinator 5k" design. As until now no one uploaded a make of this design, I think it is too difficult to print because of warping. Please let me know if this is the case.
I left the old version online in case someone prefers that over the updated design.
Happy Printing!

Recently a full 1kg spool of fresh expensive filament slipped off my standard creality spool holder on my Ender 2. I am printing on my attic next to the stairs. As I started to feed the filament (with the hatch to the stairs still open) I slightly touched the spool and BOOOM! It fell down the stairs and shattered into thousand pieces. A Kingdom for a spare Master Spool...

This inspired me for this design:

A second Spool holder for any Creality printer that you just thread onto the backside of the standard spool holder by replacing the nut. The Clou: a print in place snap in latch that locks your installed Spool. No more flying spools!

I also reduced the diameter to fit spools that don't work with the Creality version. It is also slightly longer than the standard holder enabling you to put really large spools on it. BEWARE! Print this beefy so it won't break and send your spools flying downstairs.

Might also come in handy with multicolor printers or as a storage for often used filament ect.

Also I am a big fan of the Masterspool and upcycling old spools.
This design https://www.thingiverse.com/thing:2782912 is really nice but does not fit the Creality spoolholder. But now you can use it B-3

I am always happy to see makes. B-)