The second dimension is the overall width (mm), and the first dimension is the width at the bottom / waterline.
Couldn't find my good tape measure with feet and inches !
0 - 0
1 - 180 - 255 - rails are pretty much round
2 - 340 - 410
3 - 450 - 520
4 - 540 - 590
5 - 600 - 645 - rails start to soften, with up to 1 inch of rail tuck
6 - 640 - 675/680
7 - 660 - 695
8 - 660 - 685
9 - 640/645 - 660
10 - 605 - 615 - still virtually no rail tuck
11 - 550 - 555
12 - 475 - less than 480
13 - 350 - 350 - no rail tuck / vertical rails, at the rail
14 - 230 - 230 - wide square tail
And yes, you probably want at least 5 inches thick in the middle, maybe 5"1/2. Naish 14 is 5"3/4 plus a 1/4 of deck grip, and is at least 4 inches thick down at the tail too, giving good volume to get the bum of the board lifted on the runners.
I'll rip the fin out, and try and measure the rocker later. But the Naish 14 is very straight out the back. Not much final tail rocker.
I need this device, which actually measures rocker ! But it's in Hanalei Bay, Kauai.