Keyed system for connection of filter cartridge to filter holder

A keyed system for filters and their holders, the keyed system comprising:

• a filter and a cooperating holder;
• wherein the filter has a top end comprising a filter surface with a perimeter and at least one protrusion structure on said perimeter;
• wherein the filter holder has a holder surface with a perimeter having at least one cooperating recess structure, wherein the locations of said at least one protrusion structure and said at least one recess structure are selectively locateable to different circumferential locations on said perimeters to prevent said filter from being installed in any but said cooperating holder;
• wherein said at least one cooperating recess structure includes a first recess structure comprising a plurality of axial recess portions separated by partition ridges that protrude radially between said axial recess portions, and a single circumferentially-extending recess portion having an open end near, and in mechanical communication with, said axial recess portions;
• wherein said top end of the filter comprises an axial side wall, an upper generally radial surface, a largest-diameter portion at or near a junction between said axial side wall and said upper radial surface, and a central neck upending from said upper radial surface at a longitudinal axis of the filter and having a central neck outer wall with an outer-neck-diameter;
• wherein said at least one protrusion structure is located between said largest-diameter portion and said central neck and comprises a first plurality of key protrusions that slide through a plurality of said axial recess portions of the first recess structure during axial insertion of the filter into the holder by sliding axially past said partition ridges, and, upon angular rotation of the filter in the holder, said first plurality of key protrusions all being received in said single circumferentially-extending recess portion of the first recess structure to lock the filter in said holder.