  We study the Higgs branch of 5d superconformal theories engineered from brane
webs with orientifold five-planes. We propose a generalization of the rules to
derive magnetic quivers from brane webs pioneered in arXiv:2004.04082, by
analyzing theories that can be described with a brane web with and without O5
planes. Our proposed magnetic quivers include novel features, such as
hypermultiplets transforming in the fundamental-fundamental representation of
two gauge nodes, antisymmetric matter, and $\mathbb{Z}_2$ gauge nodes. We test
our results by computing the Coulomb and Higgs branch Hilbert series of the
magnetic quivers obtained from the two distinct constructions and find
agreement in all cases.
