  Seven-manifolds of G_2 holonomy provide a bridge between M-theory and string
theory, via Kaluza-Klein reduction to Calabi-Yau six-manifolds. We find
first-order equations for a new family of G_2 metrics D_7, with S^3\times S^3
principal orbits. These are related at weak string coupling to the resolved
conifold, paralleling earlier examples B_7 that are related to the deformed
conifold, allowing a deeper study of topology change and mirror symmetry in
M-theory. The D_7 metrics' non-trivial parameter characterises the squashing of
an S^3 bolt, which limits to S^2 at weak coupling. In general the D_7 metrics
are asymptotically locally conical, with a nowhere-singular circle action.
