What Am I Looking At?

[Danmcg]

This is a pic looking down the lock cylinder tube of the steering column. at the bottom of the shaft is the sector, what is the gold part underneath it? Whatever it is moves around with a push of a screw driver. I can't seem to find in on the exploded parts diagrams i've found online. this is a 77 standard column, ( the truck is a 77, and I assume it's the original column.)