A child-resistant closure is disclosed. The closure includes: a plastic inner shell (42) and a plastic outer shell (44). The a plastic inner shell (42) has a base wall (64) and a peripheral skirt (66) which has at least one internal thread segment (68) and an angularly spaced circumferential array of external lugs (74) on the base wall (64). The plastic outer shell (44) has a base wall (46), a peripheral skirt (48), and an angularly spaced circumferential array of internal lugs (54) on the base wall (46). The inner shell (42) is received within the outer shell (44) so that the internal lugs (54) on the base wall (46) of the outer shell are disposed for engagement with the external lugs (74) on the base wall (64) of the inner shell to apply or remove the closure to or from a container neck finish. The internal lugs (54) on the outer shell and the external lugs (74) on the inner shell have opposed rounded axially facing surfaces so that the internal lugs (54) on the outer shell cannot rest on the external lugs (74) on the inner shell upon application of force to the outer shell (44). The base wall (46) of the outer shell has a peripheral portion of a first thickness on which the internal lugs (54) are disposed, and an imperforate central portion of a second thickness less than the first thickness. The base wall (64) of the inner shell has a peripheral portion of a third thickness on which the internal lugs (54) are disposed, and an imperforate central portion of a fourth thickness less than the third thickness.
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