Oh I like this topic! Fun fact, Ball Bearings are actually a SUPER important little thing and a major hallmark component of the industrial revolution. You need to be able to make really good ball bearings in order to make a rotating joint that’s just decent, and churning out perfect little spheres by the tens of thousands was one of the first tests of the modern world’s capacity to make things in industrial quantity.

Basically, a standard rotating joint (simplified) has an inner metal band, eight ball bearings equally spaced around the inner metal band, and an outer metal band that traps all the ball bearings between it and the inner metal band. This means that the two bands can be rotated with incredibly low friction and relatively low wear. This is used in basically every machine with moving parts, and trains absolutely fit that criteria.

But it’s definitely not operated with zero wear, especially in machines that are constantly operated and weigh a lot, like trains. Ball Bearings can and will wear down during operation and need to be replaced semi-frequently.

As for buying them from China… I would assume that’s totally possible, but China might not have enough stock, or they could be trying to leverage their position to sell the ball bearings at a high markup since Russia doesn’t have the ability to buy elsewhere.