unable to close casement window

Hello,

Thanks for reaching out to us! The "stem" on the operator has become stripped. Unfortunately, this is not something that can be replaced without heavy machinery and they aren't sold separately. That being said, you'll need to replace the entire mechanism.

This operator reminds me of the 39-216 Single Arm Window Crank. To confirm that this is the correct replacement, carefully compare the diagram below. 

The compatible hardware and accessories have been tagged below along with the opposite version of the operator.

Dimensions for 39-216