Are you trying to put a Deep Tuttle Fin in a Std. Tuttle fin box?
That will not work without some serious modification of the Deep Tuttle fin head.
The fin head/root is 18 mm too tall to fin and the fin will never go down into the
std. Tuttle box.
If you need to know how much shorter the screws are for a the screws needed to
put a std. Tuttle fin in a Deep Tuttle fin box are 18-20 mm longer than the stock screws.
If you have the long screws, and need the short ones, it's best to measure them, or
take a look at the fin screw chart.