An adapter for a sealing boot includes: an annular body having a radially-outward exterior surface; at least one helical thread extending radially inwardly to define a threaded interior surface and defining a plurality of roots and crests, wherein the crests extend radially inwardly a distance A from the roots; and a blocking section that extends axially across the plurality of roots and crests, the blocking section extending radially inwardly at least the distance A from the roots at junctions with the crests, and extending radially inwardly a distance B from the roots in areas between the roots and crests.