A rod is usually also classified by the optimal weight of the fishing line or in the case of fly rods, fly line the rod should handle. Fishing line weight is described in pounds of tensile force before the line parts. Line weight for a rod is expressed as a range that the rod is designed to support. Fly rod weights are typically expressed as a number from 1 to 12, written as "N"wt (e.g. 6wt) and each weight represents a standard weight in grains for the first 30 feet (9 m) of the fly line established by the American Fishing Tackle Manufacturing Association. For example, the first 30 in (75 cm) of a 6wt fly line should weigh between 152–168 grains (10–11 grams), with the optimal weight being 160 grains (10 grams). In casting and spinning rods, designations such as "8-15 lb line" are typical.