Is 3/8 the common cut out for gally hatch seal?

Looking at the photo gallery it is hard to see the notch that is cut inside for gally seal. So far I have not cut mine I wanted to make sure 3/8 is the common cut like the generic benroy plans call for. Then when I cut the ribs for the hatch they should be cut the shape of the side before the 3/8 is taken off right.
Thanks John

Thanks John