When Seimitsu set out to create a new pushbutton, they went through many steps to ensure the perfect fit and performance.   In order to hot swap common non-soldered Cherry MX switches, the metal contacts have to be seated and held down by force.  However, in their first testing, they realized these can be mis-aligned due to the movement of these contacts (as they aren't soldered).  To optimize the contact from the switch to these contacts, they added rollers to create a larger surface area of contact

These rollers are also seated in the body of the pushbutton and because they are very small, there is a chance you may lose them, so we're offering them here as well, just in case

This comes in a set of 10 units