is the 39.155 the right operator for a left opening window it is a entry guard #20755 short arm looks to be 3-3/4 long seems to be 9 inch
Tom from SWISCO responded:
August 22, 2016
That number is associated with many different parts. I don't recommend going by serial numbers alone, as they can often be unreliable. If the dimensions and style match, you should be okay.