A MnZn ferrite designed specifically for EMI suppressoin applications 
  from as low as 1 MHz up to 500 MHz.  This material does not have the dimensional 
  resonance limitations associated with conventional MnZn ferrite materials.  
  Round cable EMI suppression cores, round cable snap-its, flat cable EMI suppression 
  cores and flat cable snap-its are all available in 31 material.