  We show that three-dimensional N=8 $Sp(N)$ and $SO(2N+1)$ gauge theories flow
to the same strong coupling fixed point. As a consequence, the corresponding
orientifold two-planes in type IIA string theory are described at strong
coupling and low-energies by the same M theory background. In the large $N$
limit, these assertions are confirmed by studying discrete torsion in the
supergravity theory corresponding to membranes on $R^8/Z_2$.
