This is a replacement for any of the white keys on the Technics KN-5000 piano keyboard, and may also fit others (let me know if you try it!). First photo shows the printed version at the back and the original Technics key in front.
PLA seems to work fine for this although Nylon might result in a more durable key. In PLA this key weighs 16g as opposed to the original's 13g but there's no detectable difference in feel. After printing light sanding may be required if your printer tends to leave sharp edges or burrs but I didn't find this necessary when printed on an Ultimaker 2+
To fit this key you remove the covers (turn off and unplug first!) then press down firmly on the back of the broken key to release it from the retaining bar, squeeze in the tags and push it forward to remove. Be careful as there's a spring under there that will try to pop out. To install the new key, carefully center the spring on the retaining pillar in the print then push the key down and back to reinstall it under the retaining bar, being sure to seat the front retaining arm under the bar at the front of the keyboard.
The author marked this model as their own original creation.