Mamiya made a few SLR's back in the late 70's and early 80's with this lens. Most cameras of that era came with a 50mm or thereabouts lens when it was purchased The camera/lens had (usually) the 42mm screw thread. They were middle of the road type of lenses not bad nor where they outstanding except possibility in the build quality.
As for value think around the $10 mark. or think that you have a very cheap and effective magnifying lupe to examine negatives at close quarters