These are Microstella nuts by @Rolex. These patented elements can be screwed or unscrewed to adjust the movement’s precision. This poising process via an exclusive key means there is no need to decase the calibre. These guardians of the balance wheel’s oscillation speed, screw-shaped when developed in 1957, were perfected in 1983 and acquired the characteristic nut shape. Rolex founder Hans Wilsdorf considered these revolutionary components a brand signature, their star shape a reminder one m

The Patek Philippe Museum