12mm "retaining ring" for original Vespa PX 200, Cosa 200, and Rally 180-200 pistons.
There are two different grooves on pistons - square and round.
- The original Piaggio cylinder kit has a square-milled retaining groove, and its piston pin is secured with a retaining ring.
- Tuning cylinders from DR, Polini, Malossi, etc. typically have a round cutout. Their piston pin is then secured with a piston clip.
Piston clips with the square shape - thus "retaining rings" - are mounted / dismounted using a retaining ring pliers.
