Designed for new construction, Arlington's non-metallic FR series device and fixture boxes have interchangeable backs and extension rings that allow one box to work with almost any exterior wall finish thickness. Get everything you need - and more, without buying extra pieces separately. That's flexibility! FR101F for devices, and the FR420F and FR405F pan box for fixtures, ship preassembled and ready for installations with 1-3/8" finish thicknesses. Altering the FR101F or FR420F boxes for 5/8" or 7/8" finish thicknesses is easy! Remove the back and re-install it on the opposite side of the box for the 5/8" depth (add extension ring for 7/8").