This is a small stand alone 5v regulator. Earlier FlightOne boards (non OSD versions) are supplied 5v power from the ESC. The newer OSD boards take full battery voltage so if you are using a Millivolt (non OSD) or Revolt (non OSD) with a 32bit ESC you need to install this regulator for it to work. It can always be used for other needs when stepping voltage down to 5v
This 5v regulator is
1.3g
.6″x.4″