11/32" Truth brand operator spindle for casement operator handle

The part you're showing here is called a spline, but these cannot be replaced or repaired in any way. When these break, you need a whole new operator.

I'm happy to advise, but we would need a clear photo of the complete operator assembly in one photo so that we can use that as a reference for our search. Please let me know if that's something you want to pursue.