restrictor
/rɪˈstrɪktə/noun
1A person who or thing which restricts something.
2A device for restricting the flow of a gas or fluid, e.g. by means of a valve, narrowed orifice, use of a porous medium, etc.
Origin
Early 19th century; earliest use found in John Stuart Mill (1806–1873), philosopher, economist, and advocate of women's rights. From restrict + -or.