This is a quick-and-dirty replacement for a missing hammer on an upright piano. Video at flickr.com/photos/ranjit/5430307892/
The pictured hammers were lasercut from 1/4" poplar, glued together in pairs to be 1/2" thick and then sanded down to 0.4" to match the original hammers. The extended slot in the bottom allows you to glue the hammer onto the old broken shafts instead of replacing them, and to tilt them to the right to hit the strings at the right angle. The felt is some wool stuff from a craft drawer. Real hammer heads are mostly felt, but I made these ones mostly wood because it was easier.