This type of lock is used, just like the inner lock, to lock the rotation of the piston ring in the groove.

Side notch/Type H

Access from the side makes the pin that falls into the opening of the side lock easier to insert than the inner lock. We often encounter this type in two-stroke and old diesel engines. Sometimes it is necessary for the piston ring not to rotate with a rotating application. We use this type of lock to achieve this.
 
Euroring designation = Type H DIN ISO Designation = NE1 to NE3