M42 Male to M39 or T-mount Male to M39 Female adaptor ring. Use with adapters to convert it from M42 mount to T/T2 mount to M39 mount. Use to convert lens mounts. Male screw thread from 2 sides: 42mm ( [A] M42 thread with 1mm thread pitch size, and [B] T-tread with 0.75mm thread pitch size ).
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