A finitely generated module over the ring L=Z[t, t^{-1}] of integer Laurent
polynomials that has no Z-torsion is determined by a pair of sub-lattices of
L^d. Their indices are the absolute values of the leading and trailing
coefficients of the order of the module. This description has applications in
knot theory.Comment: 7 pages, no figures. To appear in J Knot Theory Ramification