Jonathan Stern

Does anybody have any info on Harris Savides use of (what a DP Friend told me were called) Punch Filters. Basically a 4x4,6x6 etc... ND Grad Filter where an apeture in the middle of the filter is clear, then graduates out to a determined Unit of ND. Is this the correct name for the filter? What are the units in terms of the size of the apeture? Do they come in varius units of Graduation .3, .6 etc...? Do they come in any other flavors (ie. Tobacco, color and so on)? Thanks for the Help, Jon