What Casement Operator do I Need?

Thanks for posting. Your operator certainly resembles the 39-188 and 39-187, and it's what I'd recommend; but I can't be 100% certain without knowing the dimensions. It's also a bit hard to see beyond your storm screen. In any event, you'll want to compare the dimensions listed on the 39-188 product page with your current operator to confirm it's a match. 

Ah, forgive me, I should have clarified. "Left" and "Right" handed operators are actually defined differently from manufacturer to manufacturer. Some companies define it by what side the operator sits on, others define it by what side the handle sits on, while others may define it by the direction in which the window opens. There really is no industry standard.

The best way for you to determine what operator you need is to compare your hardware to the pictures we have on our site. Does the arm face the same direction? What side are the gears on? What side has the bore? Honestly, in your picture the operator looks more like the 39-187 to me, so my apologies for not pointing that out at the outset. But double-check the orientation of the link arms just to be sure.