Zero Moment Hinge

Mechanical bearing
Connecting two solid objects
Barrel
Butterfly
Concealed
Piano
Spring
Used to control access
since ancient times
Pin
Knuckle
End play
Gauge
Pitch
Reducing or eliminating
bending stresses

Published via LexPoMo 2021 and featured in the 2021 anthology. Image: W.carter, Creative Commons CC0 1.0 Universal Public Domain Dedication