A wellhead assembly having an outer tubular, an inner tubular inserted into the outer tubular, an annular space between the inner and outer tubulars, a lock ring in the annular space, and an activation ring that axially strokes between the lock ring and one of the tubulars. The lock ring selectively locks together the inner and outer tubulars when the activation ring slides between the lock ring and the one of the tubulars. The surface of the activation ring that contacts lock ring is contoured so that an interface surface between the activation ring and lock ring when the lock ring is in its locked position, is offset an angle from an axis of the wellhead that is less than an offset between the axis of the wellhead and an interface surface between the activation ring and lock ring when the activation ring is stroking downward.