This nine inch diameter ALUMINUM blade replaces the original plastic blade. It is a big improvement over the original. It will give long life and quiet operation. The blade fastens with an old fashioned setscrew which is included. You can retire the hairpin type fastener that is used with the original blade. The hole in the blade is 5/16 inch. OH, BY THE WAY The motor and fan RHF473 at the top of this page will replace this motor and fan. You get a smaller flow of air, but a lot smaller cost.