This plastic sits on the trap door, and makes the ball path smooth and level.
The trap door mechanism is a metal base, metal plate, decal, this clear plastic and is attached to the hinge with screws.
It has a CNC machined end that accepts the trapdoor hinge and countersunk holes for the screws that hold it to the playfield. It is also the correct thickness: this plastic is thicker than a regular clear plastic.
The material is a special high-strength acrylic that we use for this application. It will not break during installation or play.