Here's a large lens board with Packard shutter fitting still in it. It measures 7 7/8in square, so just 1/8th under 8in. Lip is 1/4in thick. As you see there's a chip missing in the front from when someone carelessly took off the retaining ring, but that can be easily filled in, or you might even need a bigger hole in it anyway and will cut that part off. That reminds me, the opening diameter is 4 5/8in.
Feel free to ask question if you have them.I’m a photographer myself, and have been buying and selling equipment on here for over 20 years now. I always do my best to describe the items as accurately as I can. Take a close look at the pictures, I try to show all possible flaws there, and so in real life my items look better than on here.