M39 Lens to M42 Camera Adjustable Focusing Helicoid Ring Adapter 25-55mm Macro Extension Tube M39-M42 - AliExpress
Fotasy M42 to M42 42mm Screw Mount Adjustable Macro Focusing Helicoid – RainbowImaging
malykh.com notes: Noname Leica M-Sony FE/E close focus (helicoid) adapter
M42 Macro Focusing Helicoid Tube Adapter | Pixco - Provide Professional Photographic Equipment Accessories
Helicoid focusing explained, for mirrorless digital cameras - YouTube
Zenza Bronica Helicoid Focusing Ring Lens Adapter for S S2 EC TL - Green Mountain Camera
Andoer M52-M42(17-31) 17mm-31mm M52 to M42 Mount Camera Lens Adapter Ring Macro Extension Tube Helicoid Lens Focusing Adapter Ring for Macro Photography - Walmart.com