This is the new 10 inch Freud fine finish blade I bought for $2 at a yard sale. I want to make a blade keeper for it so I do not risk damage to a carbide tooth.
Near the 5/8 inch arbor hole you see two flat washers. Their outside diameter is right at 5/8 inch. Their inside diameter is just over 1/4 inch. They will make a nice center for the blade to hold it in place.
Step 1: Plywood Square
I have some scrap 3/8 inch plywood. I cut a square 12 inches by 12 inches. I marked the center of the piece and drilled a 1/4 inch hole.