My mistake in the previous post. I got the tolerance backwards.
The Larry Tuttle drawing gives the fin head "thickness" (the dimension that fits in the slot and need to be parallel and close tolerance on both the fin and the fin slot in the boards is:
0.620" -0.000 +0.004, so what I suggested in Feb. 2009 is correct.
Max fin head dimension is 0.624" (15.8496 mm) and the min. fin head thickness is 0.620" (15.748 mm)
There fore the slot in the board should be 5/8" (0.625") (15.875 mm) if you allow 0.0010" clearance to get the fin down into the slot.
So, based on the Larry Tuttle drawing, the size (width) of the fin slot would be 15.875mm or 0.6250" minimum.
Sorry for the error.... my laptop battery was dying and I got in a hurry.
Hope this helps,