Top quality vespa clutch nut made by Piaggio. This has a socket size of 18mm, the thread is 12mm. They are 'squashed' at the top to stop the nut from coming undone.
 
Suitable for any Vespa with a Cosa type clutch fitted, these include:
for Vespa PX125 E, PX150 E, PX200 E, EFL, MY, 2011 and 2012 Cosa and Lusso.