For any one searching for a metal air cleaner adapter ring to adapt a 5-1/8" air cleaner base to the old WCFB 4-7/32" see this site. http://www.nimac.biz/5.htm NM04 - Air cleaner adapter to use a standard 5 1/8" diameter air cleaner housing on a 4 7/32" neck carberetor. This part is machined from billet 6061 aluminum, and will not deform like the plastic ones, plus it looks a lot better. Similar to the plastic part