The M42 17mm gets upgraded with SMC coating and mechanical coupling to allow open aperture metering with Spotmatic F, ES and ES II. It was produced from 1973 to 1976
Product Code: 43842
from left to right the 3 lens variations, from the early screw mount to the Pentax K version. 
from lens to right the mount part of the lens, from early M42 to PK.
The slip-on cap is the 58mm one, the same one you can find on the first version of 28mm 3.5 M42 and on other Pentax lenses of the same age.
