Cast metal (likely aluminium) keyswitches! They have small microswitches inside of them, along with rubber gaskets (probably ultra extreme environments).
Going from the pins, likely hotswap as well.
IMG_20171219_204256606_HDR
IMG_20171219_204309591_HDR
IMG_20171219_204430458
I have about a numpads worth of the switches with date codes (1981 to 1985):
- 8120
- 8126
- 8126
- 8126
- 8126
- 8126
- 8126
- 8127
- 8448
- 8501
Album: https://www.flickr.com/gp/triplehaata/a8a2p5