2/50mm lens OKS1-50-1, PSK mount
This lens was made at Lenkinap (renamed to LOMO later) in 1961 (#612019).
It has PSK mount (probably).
It seems that it was purposed to be coupled with front anamorphic attachment or some control unit since it has guiding pin in the focus ring and couple of grooves on the aperture ring. Both controls are on the front part of the lens, and inconvenient for manual operation.
Glass is good, though it needs some cleaning.
Low price due to rare mount and inconvenient controls. If you are amateur enthusiast, it is a great chance for you to get cheap 50mm lens fr 35mm film and play with this type of image and shallow depth of field.