Electrical receptacle outlet box extenders are specially designed to work with both PVC and metal receptacle boxes. The patented rear flange allows the electrical box extender to fit snugly against the every style box to assure no gaps are present between the existing box and your newly installed extender. This feature assures the outlet box extender meets all electrical codes. Since no gaps are present when properly installed, electrical receptacle outlet box extenders have gained the listing of Underwriters Laboratory (U.L.) Electrical receptacle outlet box extenders are U.L. Listed and made from non-flammable, self-extinguishing materials. Electrical receptacle outlet box extenders are one of the only extension rings or extenders to work with every style box made which is why its the best electrical outlet box extender out there. Dont get surprised when you expose the box in the wall, with Electrical receptacle outlet box extenders, the extender will fit! Electrical receptacle outlet box extenders allow you to shim out those electrical boxes flush with the newly installed wall covering without removing or repositioning the existing electric box. This saves time and money. Why pull out the electrical outlet box? Extend the box flush with new wall covering without having to change the box or remove the device.