  Surface-plasmon-polariton~(SPP) wave propagation guided by a metal slab in a
periodically nonhomogeneous sculptured nematic thin film~(SNTF) was studied
theoretically. The morphologically significant planes of the SNTF on both sides
of the metal slab could either be aligned or twisted with respect to each
other. The canonical boundary-value problem was formulated, solved for SPP-wave
propagation, and examined to determine the effect of slab thickness on the
multiplicity and the spatial profiles of SPP waves. Decrease in slab thickness
was found to result in more intense coupling of two metal/SNTF interfaces. But
when the metal slab becomes thicker, the coupling between the two interfaces
reduces and SPP waves localize to one of the two interfaces. The greater the
coupling between the two metal/SNTF interfaces, the smaller is the phase speed.
