Top quality Lambretta series 1/2/3 & DL/GP metal speedo drive and plastic worm. 
 
Sticky's spanner's manual says - It is preferable to use plastic driven (worm) gears on all models because these then become a sacrificial component which will fail first if something jams. It is far easier to fit a new worm gear than to replace a damaged drive gear on a hub. 
 
Can be used on all standard hubs as well as internal and external and aftermarket disc brakes.