It's about the hex key for your sail batten. Something you need to know

source: https://www.seabreeze.com.au/forums/Windsurfing/General/Small-Hook-on-Severne-Batten-Fin-Key-

Quote:

"Can anyone tell me exactly what the wee hook on the Severne Batten / Fin Key is actually designed for? I don't have Severne sails myself (I like them though!) but noticed it on a short windsurf trip recently where they had some Severne sails.

I was musing as to whether it was a bottle opener (never tried), or for somehow using it to anchor the dowhaul line for rigging or ... ???"

"It's the bottle opener, cause there is nothing better than a cold beer after a great session, Cheers Severne"