Instead of a knob, the plungers feature a pull ring or a threaded pin.
The pull ring version can be operated by hand, or it can be used as an attachment point for pull cables or other actuation mechanisms.
The threaded pin version can be customized with a knob of the user’s choosing, or it can be used to attach a pneumatic cylinder for automated operation, or Bowden cables for remote actuation, or any other sort of mechanism.