  Moduli spaces of a large set of $3d$ $\mathcal{N}=4$ effective gauge theories
are known to be closures of nilpotent orbits. This set of theories has recently
acquired a special status, due to Namikawa's theorem. As a consequence of this
theorem, closures of nilpotent orbits are the simplest non-trivial moduli
spaces that can be found in three dimensional theories with eight supercharges.
In the early 80's mathematicians Hanspeter Kraft and Claudio Procesi
characterized an inclusion relation between nilpotent orbit closures of the
same classical Lie algebra. We recently showed a physical realization of their
work in terms of the motion of D3-branes on the Type IIB superstring embedding
of the effective gauge theories. This analysis is restricted to A-type Lie
algebras. The present note expands our previous discussion to the remaining
classical cases: orthogonal and symplectic algebras. In order to do so we
introduce O3-planes in the superstring description. We also find a brane
realization for the mathematical map between two partitions of the same integer
number known as "collapse". Another result is that basic Kraft-Procesi
transitions turn out to be described by the moduli space of orthosymplectic
quivers with varying boundary conditions.
