  This paper explores various differentiable structures on the product manifold
$M \times \mathbb{S}^k$, where $M$ is either a 4-dimensional closed oriented
manifold or a simply connected 5-dimensional closed manifold. We identify the
possible stable homotopy types of $M$ and use it to calculate the concordance
inertia group and the concordance structure set of $M\times\mathbb{S}^k$ for
$1\leq k\leq 10.$ These calculations enable us to further classify all
manifolds that are homeomorphic to $\mathbb{C}P^2\times\mathbb{S}^k$, up to
diffeomorphism, for each $4\leq k\leq 6$.
