I believe you call these pivot bars

A home owner from Walton, KY says:
October 25, 2020
They are for an unknown brand vinyl double hung window. They have 2 screws that secure them to the bottom of the windows.
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Bob from SWISCO responded:
October 28, 2020

This is indeed a pivot bar. Start by viewing our 26-316. Look it over and see if this matches your old part. 
Interlocking Pivot Bar
Interlocking Pivot Bar
26-316
$1.97
Pivot Bar
Pivot Bar
26-449
$1.75
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