A professional from Jamestown, NY says:
April 2, 2016
Plastic. 1 1/4" x 3/4". Large Aluminum double hung windows.
Paul from SWISCO responded:
April 5, 2016
The window slide guide you show looks like our 26-162. Please compare it to your part to confirm. Also keep in mind that these are no longer being made, so we have a limited supply.