Special macro lens for the FED 1938/1939 production. This special lens is not rangefinder coupled but goes from infinity up to 1:1 scales in continuous focusing.
The optics is the renowned Industar 10 3.5/50.
Non numbered macro lenses can be found. According to some sellers, they could have been made in 1949 or 1950.
At least two pre war series were made: with pins (written 1st on the list) and without (written 2nd). Probably to help the owner to screw or unscrew the lens.

Known serial numbers: