I have an FCL (left-handed) wood-framed casement window in my apartment. I'm looking to add an operator to it. Right now it's just a manual push open/pull close. I think I've found an option or two, but it's unclear to me what features I need. I'm also not sure exactly how to take the measurements. So:

  1. When do I need an operator with a link? For example, right now I am looking at this operator without a link, or this one with a link. Does a link just add more stability to the open movement, or is there another reason one might need one?
  2. How do I know what length of an arm I need? I assume I can just open the window to its fullest extent, then measure from the point on the sill where I would install the operator to the point on the window where I would expect the operator to connect to, but how do I know where that would be?

1 Answer 1


The pivot point for your operator is going to be off-axis from your window's hinge line. Because of that, as your window opens and shut, the distance from any single point on your window to the operator's pivot will change, which means you can't have a fixed-length arm attached to a fixed point on the window.

You can handle this in two ways:

1) Use a split arm operator, where the swung arm has a second link connecting it to a fixed point on the window. That way the two arms will flex as the window opens and shuts, compensating for the changing distance

2) Use a straight arm operator, where the end of the swung arm slides in a channel on the widow as the window opens and shuts.

Choosing the length of the arm is just figuring out the geometry. Getting it right may be difficult without some trial and error; you may consider buying where you can return the unit if it's wrong.

  • Ah, so, using a guide such as this one means you don't need a link, while using a fixed connector requires a link. Is that correct? Seems to make sense to me Commented Nov 15, 2018 at 0:52
  • 1
    Yes, that is correct. Commented Nov 16, 2018 at 15:53

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