old window crank case, no name 4inch arm, not sure how to measure screws

Thank you for writing in to us. If the operator is operating then maybe you should try a larger diameter screw. However it can't be too long or it will risk the potential of hitting the lower torque bar at the sill of the window. If a larger screw will not work, possibly use a type of Molly bolt. If you do need a replacement operator you will have to send us more photos along with the dimensions. Thank you.

Let us see a photo showing the back of the operator. Let's see the arm of the operator. Give us some detailed measurements of the distance between screw holes, as well as, the length of the link arm.

This looks close in design to our 39-061, by my eye. Review our hole spacing dimensions and let me know how they compare. Note that the link arm might be a different length than yours, but that won't matter too much. What's more important is the diameter of the hole at the end of the arm; in the case of the 39-061, the link arm hole is 1/4".

As long as the installation hole pattern and link arm hole size match then I think this would be a good option for you. See our 39-060 for the opposite side.

If the top to bottom holes line up with the 5-1/4" spacing on our 39-060, then I think you'll be okay. The bottom holes being further apart isn't ideal, but it may not be the end of the world. You could theoretically drill a new hole to get it to install. If you're okay with doing that, then I think this part is worth considering.