Fair-Rite 0431164181 Ferrite Clamp On bead, 31 material, suitable for clamping over cables up to 13.05mm diameter for RF suppression between 1 and 300MHz.  These are very effective at suppressing common mode noise in the 1 to 30MHz region if the cable to be suppressed can be wound through the core a number of times.  Ideal for use on RG8, RG213, and 400 series cables.  Also ideal for use on IEC power cables to suppress noise birdies in the HF bands from computer display monitors.

Fair-rite PN# 0431164181, These are also known as a 2X31-181P2 by other suppliers.  32.5mm L x 29mm W, 14.6mm H, ( inside diameter 13.05mm )

For more information see the Fair-rite 0431164181 Data Sheet