RE: Fin Screws
Yes, they are M6 and the lengths will be around 55-60mm and 70mm.
It's also OK to get longer ones( which are these days more standard with many of the new boards) but these must be cut down (or spacered up) to ensure you don't split the fin base head but running the deep end of the screw too far down into the fin base.
I'm not sure o fthe best US source of M6 stainless in those lengths, mostly all the longer stainless readily available in US hardware stores etc is 1/4"x20TPI. Close, but no cigar.
If you are stuck, contact our US distributor office Trident Sports, who will either have a good source they can nominate or most likely can supply these via the dealer network(etc).
Cheers ~ Ian