Part for single hung aluminum window

A quick learner from Cape Coral FL says:
I have a 60's series window balance (2920) that came out of the window last night. The balance is fine but the part pictured is broken. I looks like some sort of cam stop. It is screwed directly into the window.

I don't know what part to order to replace.

Can you help?
User submitted photos of window hardware.
Profile picture of Paul
Paul from SWISCO responded:
This looks a lot like our 18-168. Check it out and see what you think.
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