Uncoated Hitachi Ferrite Core, material SB-5S, uf = 3000. U Type #FUR5954S, Diameter 0.4", Length 2.33", Height 1.07". This U core offers an economical core design with a nearly uniform cross- sectional area. In a power ferrite material they are frequently used in output chokes, power input filters and transformers for switched- mode power supplies and HF fluorescent ballasts.