4 Inch Round 1/2 Inch Deep Pan Box Extension Ring-5 per case - - Amazon.com
Greenfield Made in The U.S.A. B001APS Series Weatherproof Electrical Outlet Box Extension, Gray - - Amazon.com
2 Pcs, 4 in. Round Pan Box Extension Ring, 1/2 in. Deep, Zinc Plated Steel Used to Mount Ceiling & Wall Lighting Fixtures to Provide Additional Wire Capacity - - Amazon.com
Morris 36510 1-Gang Weatherproof Extension Ring, gray: Faucet Aerators And Adapters: Amazon.com: Tools & Home Improvement
Orbit 5SDB-MKO-EXT Electric Box Extension Ring, 2 1/8" Deep w/MKO Knockouts - 5" Square - - Amazon.com
Hubbell-Raco 111 Extension Ring Ceiling Outlet Box, 11.8 Cu-in, 3-1/2 in Dia X 1-1/2 in D, 3-1/2" - Light Bulbs - Amazon.com
4-11/16 in. Square Extension Ring, Drawn, 2-1/8 in. Deep with Eight 1/2 and Four 3/4 in. KO's: Amazon.com: Tools & Home Improvement
Amazon.com : VILTROX Auto Focus Macro Extension Tube DG-L for L Mount Camera, Panasonic S1 S1R S1H S5/Leica SL SL2 CL TL : Electronics
Amazon.com: RANDL Industries 5" x 4" Square 5/8" Extension Ring Back Box : Electronics
Hubbell Raco 8201 4" Square Extension Ring - - Amazon.com
RACO 8203 Electrical Box Extension Ring, 1 Gang, 22.5 Cu-in, 4 in L X 4 in W X 1-1/2 in D, 4", No Color - Electrical Boxes - Amazon.com