W+F K31 Diopters...

[Guisan]

At the left or below the S-type and at the right or above the K-for Klammer=Clamp type.
These came from the same state factory as where your K31 was assembled, they were no military issue and used from the early sixties on.

[SanPedroShooter]

Sweet. How do they attach? The factory drilled and tapped them?

Ive never seen a K31 from the post military run, but I read that they were in production after the Army switched to assault rifles.