Model originally uploaded to Thingiverse at https://www.thingiverse.com/thing:4794409.

This is a spacer for a Honeywell Doorbell Push Button type DCP311 / DCP311G, which is designed to be fitted behind the original mounting plate and provides an additional 5mm clearance from the surface that it's mounted on.

My door bell push is mounted on a brick wall, and this is an experiment to try and improve the range slightly (time will tell if this works!)