The plug is made from two halves, with a spiral spring which tries to push them apart.
From the newscientist.com
Traditional mechanical watch movements use a spiral spring called a mainspring as a power source.
From the en.wikipedia.org
The spiral spring is part of the shock absorber assembly.
From the online.wsj.com
His design used a fast-beating balance wheel controlled by a temperature-compensated spiral spring.
From the en.wikipedia.org
This is because Huygens watches employed a spiral balance spring.
From the en.wikipedia.org
Huygens ran trials using both a pendulum and a spiral balance spring clock as methods of determining longitude.
From the en.wikipedia.org
He originated the flea-flicker, screen pass, spiral snap from center, spring practices and the huddle.
From the dailyherald.com
The balance spring or hairspring in mechanical watches is a fine spiral-shaped torsion spring that pushes the balance wheel back toward its center position as it rotates back and forth.
From the en.wikipedia.org
He invented the huddle, the screen pass, the flea-flicker, spring practice and the spiral snap from center.