This is the cam, the actuating shaft that has the rear brake arm fitted and goes through the casing and pushes the shoes on to the rear hub, for Lambretta GP models, It will only fit with GP brake shoes.
You can fit a Gp cam and shoes to improve any Series 1, 2 or 3 scooter as a brake upgrade as the GP cam isn't as sloppy as on the earlier machines.
 
 
Part number: LUAF508