Two RWN reducing washers are required for each knockout
RB reducing bushings are Threaded for rigid conduit and IMC
Appleton and O‑Z/Gedney offer NEER RWN reducing washers and RB flush reducing bushings. Reducing washers are used to reduce the size of a knockout or slip hole in a sheet metal enclosure to a smaller trade size. Reducing bushings are used to reduce the trade size of a tapered entry.