I don't think another reducer is the answer? I would guess they are coated with a ceramic so if there is a brush able material maybe, never heard of anyone doing it on here? The originals NOS are not cheap but that is what I am using. I run a recirculating heater with a 12-volt motor and the original switch.
http://www.flickr.com/photos/advance-design_parts_co/8129058879/in/set-72157631867396207

http://www.flickr.com/photos/advance-design_parts_co/8129352382/in/set-72157631868452754