Bridgeport 1090-1 4 To 1/2 IN Reduc Wshr, Box of 10
https://nsiindustries.com/product/bridgeport-1090-1-4-to-1-2-in-reduc-wshr-box-of-10/
The Bridgeport 4″ to 1/2″ Galvanized Steel Reducing Washer is used in pairs to reduce the size of knockout holes in a box or enclosure. The washer features raised flanges that allow for positive seating in the knockout.