This paper discusses the structural properties of various gradings in relation to the losses resulting from the traffic offered to the inlet groups. On the basis of earlier researches on optimum graded structures, an attempt is made to obtain interconnecting schemes which will provide the maximum traffic carrying capacity of the serving trunks. The performance of these interconnecting patterns under severe unbalanced loading is examined. The overall grades of service appear to be better than those of some other structures which have appeared in the literature and with which they are compared. It is observed that the sensitivity to traffic unbalance, and the difference between losses on individual groups, can be reduced. We draw conclusions from these results about the efficiency of gradings in relation to the busy matrix, and about some rules which, we think, govern the design of optimum grading structures.