What are the things called that you put on top of an alcoholic bottle and it stops pouring at exactly 1 shot?

Those are called shot pourers, shot dispensers, or jigger pourers. They have a built-in measurement that allows you to pour a precise amount of liquor, usually one ounce, which is equivalent to a standard shot.

Some shot pourers are designed to be more aesthetically pleasing, while others are more functional. Some even have a built-in "stopper" that prevents any further pouring after the desired amount has been dispensed.