I found this on the boards.co.uk site.
I don't know if you've been there already but it's great.
"The Tuttle box has straight sides and the root is a uniform 1.60 cm (.625") and the "fit" is supposed to be quite tight on the sides. The depth is set by the angles on the front and rear of the fin root. If your fin will not go all the way into the box until the root of the fin is even with the bottom surface of the board or finbox, then you need to file or sand the radius's on the front and rear of the fin to allow it to go further into the box. You do not want to alter the width or "thickness" of the root unless you are sure it's oversize. The fin gets most of it's support from the close fit between the sides of the fin root and the sides of the fin cavity in the board.
The "Deep Tuttle" configuration is the same width on the sides, but the fin root is much taller (deeper), measuring 7 cm (approx. 2 3/4") at the same point on the root that your std. Tuttle measures 5 cm.
The front and rear angles and radius are the same for the std. and deep Tuttle, the major difference being the extra 2 cm of root "height"."Cheers,
Ben
