Aerovane Mast Crane Adaptor.
Used to hold an Aerovane at the top of a mast on a small keelboat or sports boat.
Screw the Aervoane mast crane adaptor into the tapped hole in the mast crane. Then insert the rod of the Aerovane into the adaptor and hold it in place by tightening the grub screw.
Also comes with a nut so a hole can be drilled in the mast crane and then the adaptor can be held in place using the nut rather than a tapped hole.