Identifying Small Glass Tubes Containing Three Tiny Ball Bearings

 You might have found small glass tubes containing three tiny ball bearings. These aren’t random trinkets—they’re precision components from antique spirit levels, often called bullseye or machinist’s levels.  What They AreUnlike standard levels with a single bubble in a curved tube, bullseye levels feature a circular, dome-shaped capsule filled with liquid, measuring levelness in two directions at once. In some older European or industrial models, the usual bubble was replaced—or supplemented—by steel ball bearings. These balls roll to the lowest point, giving a clear visual cue of true level from multiple angles.  Why Ball Bearings Instead of a…