Identifying Small Glass Tubes Containing Three Tiny Ball Bearings: What Could They Be?

indicator or sensor assembly

It is important not to assume that the object is a particular device simply because it contains three metal balls. Similar-looking parts can serve very different purposes.
Possible Identifications

Let’s look at some categories that might help explain what you’ve found.
1. A Mechanical Indicator or Moving-Ball Component

Some mechanical devices use small metal balls that move inside a narrow housing. Their movement may help indicate orientation, motion, vibration, or the position of a component.

A glass tube could allow someone to observe the movement of the balls.

Clues to look for: Do the balls roll