Our PGM parallel grippers are always delivered with 6 centering rings (2 per jaw and 2 for fastening the gripper).

Depending on the structural conditions (space available), versions with gripping force or spreading force locks are available.
It is implemented using spring force. Since the spring is located on the outside of the gripping force locks, this option can be retrofitted (accessory).

Here you can find the mechanical spring forces per PGM size as a PDF file for:

The spreading force is secured by a compression spring - jaws are mechanically pressed apart.

Gripping force is secured by a tension spring - jaws are mechanically pulled together.

Since the gripper always has to work against the mechanical forces of the spring, the spring forces are deliberately smaller than the pneumatic forces - especially since in the majority of cases the gripping is positive or partially positive.