Plug lock
From Halopedia, the Halo wiki
Summary
The Forerunner's constructed massive plug locks that are required to be disengaged in order to deactivate the Containment Shield in the Sentinel Wall. All four plug locks have to be disengaged or the Shield remains in place. The plug locks are well defended by Sentinels and Enforcers to keep the locks from being disengaged.
To disengage the plug locks, they must be struck or hit. Alternatively, one can "press" them if playing on the Easy or Normal difficulties.
