Steel Hydraulic Coupling Plug 14 mm S Cutting Ring ISO 14540/8434-1 D M32 x 3 | Tameson.com
Amazon.com : 52mm-52mm Male-Male Thread M-M Macro Photography Lens Coupling Ring for Mounting Two (2) Lenses Face to Face : On Camera Macro And Ringlight Flashes : Electronics
77792 Coupling Ring
Atra-flex M5 RING Coupling Ring + 2 M5 HUB QD F* | eBay
Adlake 4 1/2" Coupling Ring — The Source for Oil Lamps and Hurricane Lanterns %
Macro Reverse Ring for Lens to Lens Coupling - Filter Thread to Filter – Fotodiox, Inc. USA