Let ε = (ε 1 , . . . , ε m ) be a tuple consisting of zeros and ones. Suppose that a group G has a normal series of the formfor ε i = 0, and all factors G i /G i+1 of the series are Abelian and are torsion free as right Z[G/G i ]-modules. Such a series, if it exists, is defined by the group G and by the tuple ε uniquely. We call G with the specified series a rigid m-graded group with grading ε. In a free solvable group of derived length m, the above-formulated condition is satisfied by a series of derived subgroups. We define the concept of a morphism of rigid m-graded groups. It is proved that the category of rigid m-graded groups contains coproducts, and we show how to construct a coproduct G•H of two given rigid m-graded groups. Also it is stated that if G is a rigid m-graded group with grading (1, 1, . . . , 1), and F is a free solvable group of derived length m with basis {x 1 , . . . , x n }, then G • F is the coordinate group of an affine space G n in variables x 1 , . . . , x n and this space is irreducible in the Zariski topology.