  We study the T duality between a set of type IIB D3 branes atnon-orbifold
threefold singularities, and type IIA configurations of D4 branes stretched
between relatively rotated NS fivebranes. The four-dimensional N=1 field
theories on the D3 brane world-volume can be easily described using the IIA
brane configuration. These models include families of chiral theories
continuously connected to the theories appearing in brane box models (or D3
branes at orbifold singularities). We propose that phase transitions in the
K\"ahler moduli space of the singularity are related to the crossing of rotated
NS fivebranes in the T dual picture, and thus to Seiberg's duality in one of
the gauge factors. We also comment on the inclusion of orientifold planes in
the IIA brane picture.
