Jalousie window crank for a Hexagon shaft

I am a bit new to the vintage camper scene so pardon me if my question has a obvious answer... I have a 1958 Citation that has jalousie style windows and has a 5/16"(flat to flat side) Male Hexagon shaft(no threaded hole in the end) protruding out for the handle, the camper did not come with any cranks so I started searching a while back and find only spline style cranks... What gives?

I could make something out of a old socket and TIG up a handle and just keep it in a drawer but would prefer to have something proper for the job.

Anyone know of a supplier of such an animal?

Thanks

Sorry no pic at this time... I haven't signed up with Flickr yet