A pin-box well tubular connector assembly having pin and box connector members (6, 5) with intermeshing external and internal screw thread profiles is optimized for expansion downhole in a wellbore by: A) configuring the box connector member (5) such that it has at least one thread (10) that does not engage a thread on the pin member (6); and optionally: B) configuring the pin and box connectors (6, 5) such that in axial direction a gap of at least 0.2 mm is present between the external and internal screw thread profiles; and/or C) inserting a swellable dope in the gap between the pin and box connector members (6, 5).