  By imposing axial and vector Ward identities for flavour-non-singlet
currents, we estimate in the quenched approximation the non-perturbative values
of combinations of improvement coefficients, which appear in the expansion
around the massless case of the renormalization constants of axial,
pseudoscalar, vector, scalar non-singlet currents and of the renormalized mass.
  These coefficients are relevant for the completion of the improvement
programme to O(a) of such operators.
  The simulations are performed with a clover Wilson action non-perturbatively
improved.
