Hi Shane
It’s a speedo drive gear
Normally these were found on earlier wheels fitted to k series models - 1939 season
The outer brake place is from later W models. 1940 onwards which is what makes the set up you have an oddity - the drive gear looks meaningless
It needs the earlier brake plate which has an aperture which has the speedo gearbox mounting fittings on it
Nice find & a scarce wheel to have