A locking grating or seal for a conduit includes a cover positioned at one open end of the conduit and is removably engaged and axially aligned with, an expander positioned within the conduit. A jacking bolt penetrates the cover and the expander, and is threadedly engaged with a jacking nut in a position within the conduit and spaced apart from the expander. C-shaped elastically flexible arms are integrally engaged with the expander and with the jacking nut so that rotation of the jacking bolt enables the jacking nut to move toward the expander forcing the C-shaped arms to bow outwardly into contact with the conduit for gripping it.