Replacement crank for casement window question

A handy person from Austin, TX says:
I have three casement windows on a condo built in 1980 that are missing cranks. The windows are aluminum, and there are no markings anywhere to signal what brand they might be.

The spline appears to be 3/8", but I tried ordering the following product (H-3966 fits Andersen from Prime-line), and it was loose. I couldn't tighten the screw enough to make the ridges catch the grooves inside the handle, and the spline was also too long for the shaft inside the handle.

The length of the shaft is about 3/4".

The spline has 2 sets of 11 ridges at the top as well as a 3rd row near the base.

Any suggestions are much appreciated!
User submitted a photo of a window operator.
Profile picture of Dave Sr.
Dave Sr. from SWISCO responded:
It looks like this is a Pella operator, not Andersen. Can you confirm? Look at our 39-109B handle. This is used for Pella crank operator's 3/8" splines. This could be the handle you are looking for.
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