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.
Step 2: Attach a screw, the washers, and a nut
I inserted a 1/4 inch x 1 inch round head screw into the hole. I placed the washers on the screw and added a low profile (thin) nut. I tightened the nut. The washers now center the blade and hold it in place.
Step 3: Make a small square of plywood
I cut a square 2 inches on each side from some of the 3/8 inch plywood. I marked the center and drilled about halfway through the plywood with a 3/4 inch spade bit. This makes a recess for the nut on the screw so the surface of the 2 inch square will mate with the face of the blade and hold it securely. When you are sure the recess is deep enough to cover the nut, drill out the center of the hole to a little over 1/4 inch.
Step 4: All done
Turn the 2 inch square over and place it on the screw. Add a wing nut and tighten finger tight.
I could make my blade keeper more decorative by giving it eight sides or rounding edges, even painting it. But, it works well as it is, and my blade is protected.