Please be aware that the price is specified for 1 unit, not for a set of 3!
The price is a subject to future changes.

Ball transfer unit, designed specifically for trackballs.

Allows to make precise, pixel-based movements from the steady state.

Comparing to BOSCH® Rexroth BTUs, these are:

• Much quieter, however there is some sound when the bearing balls rearrange themselves inside. It is possible to operate the BTUs without this effect, completely silent, but only slowly.
• Less consistent — the Rexroth BTUs have pretty much perfectly identical friction no matter if it's steady state or mid-gesture. These ones, however, have very low static friction, which slightly increases at the beginning of a gesture, and then falls back to the level which can be described as "noticeably better than static bearings".
• Don't require lubrication, and can be cleaned with a thin hair toothbrush or with compressed air.
• Can be "repaired" — as in, you can pull the load ball and the bearing balls out and replace all of them or just some.

These are highly experimental, and there isn't any data/statistics on the long term use. The internal dimensions are a subject to change; currently, a BTU consists of 16* 3 mm silicon nitride bearing balls and a 5.8 mm G10 steel load ball.