Simple, small, and robust earplug case with a strong pinch/twist style snap lock. I specifically made this to fit my ER20xs and have quite a robust latch to avoid accidental opening. This should however fit a range of generic small earplugs or other small thing you may want on your keyring securely.

If you print in PC I find you must move the hinge through its range of movement soon after the print is complete else it can bind, sometimes hitting the hinge with a blowtorch gently and moving it can unbind them.