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

of an older instrument. The tube’s construction, markings, and the way the balls move are needed for a more confident identification.
Are the three balls actually ball bearings?

They may be, but appearance alone cannot confirm that. True ball bearings are precision-made components designed to reduce friction in mechanical assemblies. Small metal spheres can also be weights, decorative pieces, or other moving parts.
Why would an object contain exactly three metal balls?

Three balls may be used for a particular mechanical arrangement, a demonstration, or a decorative effect. The number alone does not reveal the object’s purpose.
Should the balls