  We solve a long standing problem on the computation of the Higgs branch
$\mathcal{H}$ of linear quivers with 8 supercharges and with both unitary and
special unitary gauge nodes. The solution uses the concept of magnetic quivers,
where components of $\mathcal{H}$ are described as 3d $\mathcal{N}=4$ Coulomb
branches. When the starting quiver is good, there is a single component in
$\mathcal{H}$ and the magnetic quiver is a 3d mirror. The magnetic quivers are
obtained from studying the brane web for an auxiliary 5d theory (with only
special unitary gauge groups), constrained by a new notion called brane
locking, where some branes are required to move together. We view this as a
computational tool rather than an operation in 5d. A detailed algorithm is
given, and implemented in a code available for download.
