We report explicit results for the zero-field correlation length, <(T; L), of a spherical-model ferromagnet confined to geometry C'"'x me (d>2, d'<2) and subjected to 'twisted' boundary conditions. In the region of first-order phase transition (T< T-), 6 under 'twistcd' boundary conditions obeys the same scaling law as under periodic boundary conditions, though with a different amplitude. In the 'core' region (T= TJ, the scaling behaviour changes radically as one moves from one set of boundary conditions to the other-affected greatly by *e 'pinning' of the ground-state wavevector ko of the system.