The airsoft tappet plate is a key component in airsoft electric guns that synchronizes a compression cycle to the BB loading mechanism and ensures that a BB is loaded into the hop-up chamber each time a cycle is initiated.
The tappet plate acts as an arm that connects the air seal nozzle to a timing cam on the sector gear in a gear set. As the sector gear rotates the cam pulls on the tab on the tappet plate pulling the air seal nozzle back. This allows BBs that were once blocked by the air seal nozzle to rise up from the magazine and line up with the hop-up chamber. As the sector gear continues to rotate the cam and the tappet plate returns to its original position which pushes the air seal nozzle and the BB in front of it forward into the hop-up chamber.