Length of extension arm

I am afraid I'm not certain of the length of the link arm on the 39-256B. However, I should note the exact length of the link arms is honestly not too important for these types of awning operators. Their design allows for a sufficient amount of play that it doesn't need to be exact. The hole spacing on the top and bottom tabs, as well as the hole at the end of the link arm and its overall style, are much more important. If in doubt, send us pictures of your old operator out of the window and I'll try and confirm what you need. 

I had one of my colleagues in our warehouse check. The distance between the center of each mounting hole on the link arm of the 39-256B is 2-1/8". Again, I stress that with awning operators the exact length of the arms almost always is not important. There's play with how these folds that prevents them from being an issue with the window. You could always try the 39-256B, and if by chance it proves not to work, view our Return Policy here.