Asahiflex Microscope Adapter
This is a rare accessory that was produced for use with Asahiflex cameras. The microscope adapter is made from heavily chromed brass and has M37 mount threads. When Asahi switched to M42 mount they remade this adapter with M42 mount. The construction remained identical with the only difference being that the main tube was made with anodized aluminum. Last image shows Asahiflex M37 version next to its M42 version.
Asahi Pentax Helicoid Extension Tube / Variable Close-Up Ring