Sting fin

Hi I have a 6"8 x21x3" sting with no fin what size  fin should I use in it 

Eh,

Silly rabbit!

measure from center/center of fin box to rail edge.

= length.

But most singles will work…

Thank you very muchly rode this  morning for the first time with a 6" fin was to small will measure and try again

Measured a few of my singles, and I run about 20% more length then mid box to rail. I do tend to surf more off my front foot though.

If you want to go Rubberman style it’s gotta be all the way forward and a little loose in the box for extra snap.