This brush holder is designed to snap onto the rim of a one quart paint can (about a litre), I have no idea how standard paint can rim profiles are, but the can in the photos has an inner rim with a radius of about 40 mm. The width across the rim is about 14 mm. I printed this on its side with support. The scarring caused by the removal of the support material leaves a nice texture on the inside of the bunny ears that helps to grip the brush. This is sized to grab a 10 mm thick brush. The Fusion 360 file is included if you want to modify.

This thing installs by catching the outside rim of the can and pushing forward. It is removed by lifting the outside tab and pushing forward.

Afterthought: This thing may require an occasional tune up, The "bunny ears" loose their gripping force after a while. I give them a blast of hot air with a hair dryer and squeeze them together to improve their grip. You may have better luck printing with ABS or PETG.