Oops my bad. I was looking at a 6.5 initially, but then ended up getting a 10" - https://smile.amazon.com/dp/B07RDDKH36/ref=cm_sw_r_apan_i_G6R1MW0N49S64J9WVRGN?_encoding=UTF8&psc=1

Because it's not an F2 , there isn't a 35mm "ledge" that extends over the fin box, and the screw doesn't lock as is - needed to add a washer that sits on top of the box to pull back on the bolt and lock the fin in.... :/