Piston locking tool (short version) -M14 x 1.25- (type NGK E-spark plug) - Vespa Smallframe V50, PV, ET3, PK, Largeframe PX, T5, Cosa, Sprint, Rally, VBB, Wideframe V1-15,V30-33, VL, VB, ACMA, Lambretta LI, SX, TV, GP

This can block the piston. Is often used for ignition adjustment with the envelope measuring method.