Southwire 4 in. x 1 in. Metallic Steel Switch Box Extension Ring Box Conduit Fitting Accessory SBEX-UPC - The Home Depot
RACO Silver Steel New Work/Old Work Standard Box Extender Wall Electrical Box in the Electrical Boxes department at Lowes.com
ReceptXtenders Receptacle Outlet Box Extender, Electrical Outlet Extender for Electrical Box and Electrical Outlet Switches, UL Listed - 1/2" Single Gang 5-Pack - Amazon.com
Carlon Multi-Gang PVC Electrical Box Extender (2-Pack) B1MGEXT-2 - The Home Depot
ReceptXtenders 1/2 in. 1-Gang Electrical Receptacle Box Extension Ring 00004 - The Home Depot
ReceptXtenders Receptacle Outlet Box Extender, Electrical Outlet Extender for Electrical Box and Electrical Outlet Switches, UL Listed - 3/4" Single Gang 5-Pack - Amazon.com
RACO 8203 Extension Ring, 1-1/2 in L, 4 in W, 1 -Gang, 12 -Knockout, Steel, Galvanized
3 Gang Electrical Box Extender Goof Rings Add Up to 1.5'' Deep
Raco 653 4" x 2" Handy Box Extension, 1-1/2" Deep, 1/2" End Knockouts, Welded | Quality Electrical Distribution (QED)