For the purpose of building a new top, thicker is better. I swapped rails on my MFT and had to cut and bore a new top. I used Chinese ply which is a little thinner. The reason to use ply instead of mdf is a significant weight difference. The post that the lock down knobs on the miter rail must be 3/4" so when the miter rail is attached it will not tighten properly without washers. I have to rebuild my top soon and will be using a little thicker material. Chris