The Cantex 4 in Poly Plug, Ribbed, Tapered (5315252, Millennium part 523438) seals the open end of 4 in Schedule 40 or Schedule 80 conduit to keep dirt, rodents, and water out of duct that's been placed but not yet cabled. Its ribbed sidewalls grip the duct ID for a tight, tool-free fit, and the tapered body pulls out cleanly when it's time to blow cable through. It works across EB and DB duct applications on the same job site. Millennium stocks matching plug sizes from 1 in up for capping duct banks of any diameter.