  Using domain wall fermions, we estimate $B_K(\mu\approx 2 GeV)=0.628(47)$ in
quenched QCD which is consistent with previous calculations. At $\gbeta=6.0$
and 5.85 we find the ratio $f_K/m_\rho$ in agreement with the experimental
value, within errors. These results support expectations that $O(a)$ errors are
exponentially suppressed in low energy ($E\ll a^{-1}$) observables, and
indicate that domain wall fermions have good scaling behavior at relatively
strong couplings. We also demonstrate that the axial current numerically
satisfies the lattice analog of the usual continuum axial Ward identity.
