Protective cap for CO2 cartridge

I use CO2 cartidges to inflate bicycle tires on the go. However I was afraid that the sharp edges of the threads might damage my backpack or the tube (I have a cartridge strapped together with a tube right at my bicycle frame).

This cap covers the threads, is easy to print and quick to put on or off.

I used PET-G, but other durable filaments for outdoor use might work as well.