  We calculate the ring structure of the singular instanton Floer homology of
$(S^1\times \Sigma, S^1\times \{p_1,\dots,p_n\})$ with C-coefficients, where
$\Sigma$ is a closed oriented surface. As an application, we prove an excision
formula for singular instanton homology when n=1. This settles the last unknown
case of excision formula for instanton Floer homology.
