Part of the Donkey/ Buffalo handle locking mechanism. The handle lock is made up of a Release button that pulls up on this actuator via a connecting cable. The actuator is held in the rest/ locked postion by a spring, when the release button is pulled up the cable makes the actuator turn. Three prongs of the actuator push against three ramps on a thrust disk. the thrust disk then moves the locking cog inward releasing the handle.
Note Bugaboo denotes Left and Right from the front of the stroller.