Simonton window crank handle

I'm afraid I don't know what handle will work with this operator, exactly. Your photos only show the base of the operator, which is unfortunately not enough for me to identify what it is or what hardware may be compatible with it.

If possible, can you show me a photo of the complete operator mechanism? If there are any names or branding info printed on the operator arms, that would help, too; most window manufacturers like Simonton outsource hardware like this from other companies.

Lastly, can you tell me the diameter of the spline? You'll need to take that red cap off of it, first. That's not an important component, that just protects the spline during shipping, so it can be safely discarded.