  We construct M-theory curves associated with brane configurations of SU(N),
SO(N) and $Sp(2N)$ 5d supersymmetric gauge theories compactified on a circle.
From the curves we can account for all the existing different SU(N) field
theories with $N_f \leq 2 N$. This is the correct bound for $N \geq 3$. We
remark on the exceptional case SU(2). The bounds obtained for SO(N) and
$Sp(2N)$ are $N_f\leq N-4$ and $N_f\leq 2N+4$, respectively.
