This tool locks into the cut out on the rear section of the dynamo pulley , making it alot easier to undo the 21mm nut 
(In the other listings we also do the 21mm spanners on there own) 

This tool is for the 108mm Diameter sized pulleys (We also sell them for the later larger diameter 99mm pulleys , see our other listings)

These are made from a tough tool steel then Zinc passivated . 

Please note VW made 2 sizes of pulley a 99mm diameter and a 108mm so just measure your pulley across the front face to know what size you have before ordering . 

This is for a 99mm pulley