Print-in-place design - just put it through your slicer and don't worry about supports. All around clearences is around 0.25mm, but I was successfull with my shitty old Ender 3 Pro so you should be able to just pull it open without much force after printing. 

(Keep in mind that a big elephants-food will fuse the parts together on the first few layers.)

This tool is used to mute single strings while tuning the treble section of a piano.

The only thing you'll need is a spring that keeps the tension. I've used an old Ender 3 spring for it, the recess for the spring has a diameter of 8 mm, but literally every spring should work if you just glue it in the hole.

I've printed it in PLA, but it should work with every not-soft-material.