MODEL U25:This offers impedance (peak approx 300at 2- 300MHz) with negligible impedance below 1MHz. Plastic case measures 32L x 30mm square. It will take a lead up to 12mm (1/2) diameter but preferably 10mm. Basically a split high permeability ferrite core with a plastic case, these devices are ideal where parasitic voltage spikes are a problem or potential problem. The cores come in a hinged plastic case, simply snap on to the computer or data cable.