28x Ferrite Cable Cores Laird Performance Materials 28x Ferrite Cable Cores come in four variants: split/snap-on (28A), cylindrical (28B), solid core (28R), and split core (28S). The 28x ferrite cable cores are constructed from ultra-thin mixtures of iron, nickel, and zinc oxides. They are available in cylinder, ribbon, split-flat, and clamp-on shapes. Laird Performance Materials 28x ferrite cable cores provide excellent differential and common mode EMI suppression on flat cable assemblies.