self-stopper
nounUK /ˌself ˈstɒpə/
US /ˌself ˈstɑːpər/
A self-stopper is a thing that stops itself without anyone helping it.
The toy car has a self-stopper so it stops before hitting the wall.
OTHER MEANINGS
2. A person who stops themselves from doing something, like eating too much candy.
She is a self-stopper and never eats the whole bag of sweets.
3. A device on a machine that turns it off by itself when something goes wrong.
The washing machine's self-stopper cut the power when the door opened.
4. A cap or plug that closes itself after something goes through it.
The bottle has a self-stopper so the water does not spill out.