Which Operator
It's entirely possible you bought the wrong part, but I can't confirm based on this photo. I need to see a picture of the original operator out of the window in order to find the best match for it.
Thanks! This operator here is definitely our 39-188. That would definitely be my recommendation.
I'm very sorry to hear about that. I don't believe they make that 4" arm anymore, unfortunately. The 5" is the closest size that we have.
If you're handy, you could swap the arms out. What I usually do is drill the arms out, then install the old arm on the new operator using a rivet like the 62-014, or any equivalent you can find at a hardware store. Would that work for you>