This paper presents a generahxation of the previously reported matched abundance-ratio cascades for multicomponent isotope separation. Matched abundance-ratio cascades match the abundance ratio of two components, called key components, of the proces& mixture wherever streams are mixed. The new cascades, called constant key weight cascades, are matched abundanceratio cascades with dummy key components. Formulae for the resolution of the productivity of a three-stream constant key weight cascade are given; these formulae elimmate iterative computations previously necessary to balance out the cascade in al1 components. It is found that the separation characteristics of constant key weight cascades are conveniently controlled by the key weight, which is the arithmetic mean of the molecular weights assigned the dummy key components; examples are given. Permitted variation of the key weight is also of use in cascade optimixation, and this is briefly discussed both for an "end component" and a "middle component" separation.