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I wanted modify a pinball playfield's backboard with a light feature behind the volcano by installing a playfield insert but didn't want to fuss with drilling to a particular depth. I simply drilled all the way through the ply with a 1 inch spade drill and then created an accurate insert stop that still allows the globe light to pass through the centre. It is designed to suit a ply backboard that is 13.50mm thick. and held in place with 2 typical screws used on play fields.
To do this mod you need to install a new backboard decal as well.