Help with 2 piece sliding brass item marked A1 & A2

[bologna321]

Found this in a park near some old railroad tracks. I think the dirt may have been brought in from somewhere so it may not be railroad related.

The knob seems knurled like you could loosen or tighten by hand.

 

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[Goldiver]

This piece reminds me of the part on a hand plane that holds the blade down.

Steve