Casement window part

Thanks for posting. It looks to me like you have a dual-arm operator, but the arm that should attach to that 39-416 stud bracket on the sash is missing. Most likely this operator is either the 39-031 or 39-155. If there's an identical window in the house, I'd check it to see which you need. The 39-031 and 39-155 are very similar, but the link arm dimensions are slightly different. See the photos below for reference. In either case, for a new handle and cover, see the 39-107 and 39-114L sold separately.

Dimensions for 39-031

Dimensions for 39-155