We investigate global symmetries for 6D SCFTs and LSTs having a single
"unpaired" tensor, that is, a tensor with no associated gauge symmetry. We
verify that for every such theory built from F-theory whose tensor has Dirac
self-pairing equal to -1, the global symmetry algebra is a subalgebra of
$\mathfrak{e}_8$. This result is new if the F-theory presentation of the theory
involves a one-parameter family of nodal or cuspidal rational curves (i.e.,
Kodaira types $I_1$ or $II$) rather than elliptic curves (Kodaira type $I_0$).
For such theories, this condition on the global symmetry algebra appears to
fully capture the constraints on coupling these theories to others in the
context of multi-tensor theories. We also study the analogous problem for
theories whose tensor has Dirac self-pairing equal to -2 and find that the
global symmetry algebra is a subalgebra of $\mathfrak{su}(2)$. However, in this
case there are additional constraints on F-theory constructions for coupling
these theories to others.