28A Ferrite Clamp Filters Laird Performance Materials 28A Ferrite Clamp Filters are split, snap-on cores in plastic cases for broadband EMI filtering. The 28A Series is designed for round cables and wiring harnesses. For retrofit and post-assembly operations, Laird offers a selection of 'split' cores that are similar in performance to the one-piece core designs. The 28A split ferrite cores provide excellent common and differential mode EMI suppression on round cable assemblies. Lightweight plastic snap-on cases provide the secure closure of the split cores onto the cable. The cases are available in black or white with dimensions ranging from 5mm (0.197') to 56.63mm (2.23').