4" speaker box

This is a speaker box thingy that I made to mount a pair of 4" speakers on the parcel shelf in my car without cutting holes.
There is a flange on either side of the box to make a screw hole as applicable, but I actually ended up hot gluing the boxes to the parcel shelf. Be warned that if not properly secured, anything loose in the car can become a lethal projectile if an accident were to occur.
The outer diameter on the mounting surface is the same as the grille that came with my speakers, witch are branded "Biltema".