A quick learner from Boalsburg, PA says:
August 18, 2016
The plastic end pieces are broken. Window size is 31 5/8 x 38. It is the type window that you open the flip down to wash. I have attached a picture of the label tat was on the window sash. The number horizonal on the metal part is 18C and letters facing vertical are BSI and letters facing horizonal after the letters are LC. I hope this and the picture helps in determining the parts I need. I will need complete parts for three windows.
Tom from SWISCO responded:
August 19, 2016
Please see our Series 775 channel balance, this appears to be a possible match.