HI. The directions mention the length of the 2x6 for the slabs to be 50 inches but it doesn’t say what the width is. I’m guessing it is 17.5 inches seeing the 2x6 sits inside the 50 inch pieces giving it a 21.50 inch width?
Hi Michael and welcome to the BrickWood forum.
I did look back at the instructions for the bases (there are two, and the one you build depends on which version of the oven you’re building). BrickWood does not explicitly give a measurement as you said.
But here’s a case where you wouldn’t really want that. You have the measurements for the OSB bottom and the length. But the width needs to be measured once the two long lengths are in place. Any bit of variation in how your lengths are fastened to the OSB will affect the length of the two inside boards.
Properly, you should not precut those, but use your square and rule to measure once the two long pieces are fastened.
Hope this helps, and let us know how you make out!