Let G be one of the classical
groups GL(n), U(n), O(n) or Sp(2n), over a nonarchimedean local field of
characteristic zero. It is well known that the contragredient of an irreducible
admissible smooth representation of G is isomorphic to a twist of it by an
automorphism of G. We prove that similar results hold for double covers of G that
occur in the study of local theta correspondences.