Abstract: A filter and its holder each have a keyed surface, one being a protruding “key” and one being a recessed “lock,” wherein cooperation of these keyed surfaces is required in order for the filter to be installed in the holder. Modification/adaptation of the keyed surfaces, by changing the location, number and length of the key protrusions and cooperating recesses during manufacture, allows various sets of mating filters and holders to be produced so that only mating/matching filters and holders may be connected together. The keyed protrusions are preferably located on an upper shoulder or on protruding flange(s) of the upper end of the filter. The cooperating recess structure inside the filter holder comprises axial recesses that allow axial insertion of the key protrusions, and hence the filter, into the holder and also a circumferential recesses portion that receives multiple key protrusions to retain the filter in the holder.