This is a helicoid adapter for attaching to M42 mount lenses. It supports M42 to M42 mounts. 10mm-15mm This adapter is for adjusting the flange back, to be attached before lenses without a focus ring or mount conversion adapters. Because it is thin, if done well, you can create a mount adapter that is more compact and looks better than commercially available helicoid mount adapters. It has only been used once and is almost a new product. This product is for those who have a deep understanding of old lenses and custom-made adapters. It is intended to be used to understand the flange back of the corresponding lens and to compensate for the missing focal length with this part, so I would like those who know something about it to purchase it. I do not have the knowledge to know the focusing distance and flange back for each lens, so I cannot answer questions such as "Can I attach this to this lens?" or "Can I compensate for the flange back by attaching this to this lens?". I recommend that you research before purchasing. Immediate purchase is welcome. It will be sent by anonymous delivery to prevent it from getting wet. Old lens lens adapter mount adapter Extension tube extension adapter Extension helicoid tube helicoid Helicoid adapter custom lens custom adapter Adapter production adapter focus helicoid tube Focus helicoid tube adapter Focusing helicoid adapter k&f k&fconcept focal point studio M42 mount M42 screw mount M42 screw mount