Two-gang switch box - 88mm

I needed a fairly deep switch box in order to finish up a project of installing speaker wires and a fiber optic line to an uninsulated garage.  The support on the back of the fiber cable prevents it from being installed in a standard 50mm box.  I first printed a 30mm extension, but decided it was easier to print a whole new box.  I've included the extension here as well, for people who want to go that route.  The electrical box I bought has several sets of holes, so I used holes in the corners to attach the extension, and the holes more centered, to install the keystone plates.  I only needed the one opening in the bottom, and didn't need it threaded.