  We present a detailed theoretical study of the electronic spectrum and Zeeman
splitting in hole quantum wires. The spin-3/2 character of the topmost
bulk-valence-band states results in a strong variation of subband-edge g
factors between different subbands. We elucidate the interplay between quantum
confinement and heavy-hole - light-hole mixing and identify a certain
robustness displayed by low-lying hole-wire subband edges with respect to
changes in the shape or strength of the wire potential. The ability to address
individual subband edges in, e.g., transport or optical experiments enables the
study of holes states with nonstandard spin polarization, which do not exist in
spin-1/2 systems. Changing the aspect ratio of hole wires with rectangular
cross-section turns out to strongly affect the g factor of subband edges,
providing an opportunity for versatile in-situ tuning of hole-spin properties
with possible application in spintronics. The relative importance of cubic
crystal symmetry is discussed, as well as the spin splitting away from
zone-center subband edges.
