An air filter cartridge comprising: (a) a media pack having an inlet flow face and an opposite outlet flow face; (i) the media pack comprising a plurality of flutes extending between the inlet flow face and the opposite outlet flow face; and, (ii) the media pack being closed to passage of unfiltered air therethrough, between the inlet flow face and the outlet flow face; (b) a seal member adjacent the outlet flow face and including a radially outwardly directed radial seal surface; and (c) a preform support positioned on the media pack adjacent the inlet flow face; (i) the preform support including a first member of a first projection/receiver arrangement thereon; the first member including a first projection member (295, 377) including first and second sidewall sections having portions non-parallel and diverging from one another; (ii) the preform support includes a first projection member of a second projection/receiver arrangement thereon; the first projection member of the second projection/receiver arrangement including first and second sidewall sections having portions non-parallel and diverging from one another; (iii) the first projection member of the second projection/receiver arrangement is shaped and positioned as a mirror image of the first projection member (295, 377) of the first projection/receiver arrangement with the media pack positioned therebetween. (a) a media pack having an inlet flow face and an opposite outlet flow face; (i) the media pack comprising a plurality of flutes extending between the inlet flow face and the opposite outlet flow face; and, (ii) the media pack being closed to passage of unfiltered air therethrough, between the inlet flow face and the outlet flow face; (i) the media pack comprising a plurality of flutes extending between the inlet flow face and the opposite outlet flow face; and, (ii) the media pack being closed to passage of unfiltered air therethrough, between the inlet flow face and the outlet flow face; (b) a seal member adjacent the outlet flow face and including a radially outwardly directed radial seal surface; and (c) a preform support positioned on the media pack adjacent the inlet flow face; (i) the preform support including a first member of a first projection/receiver arrangement thereon; the first member including a first projection member (295, 377) including first and second sidewall sections having portions non-parallel and diverging from one another; (ii) the preform support includes a first projection member of a second projection/receiver arrangement thereon; the first projection member of the second projection/receiver arrangement including first and second sidewall sections having portions non-parallel and diverging from one another; (iii) the first projection member of the second projection/receiver arrangement is shaped and positioned as a mirror image of the first projection member (295, 377) of the first projection/receiver arrangement with the media pack positioned therebetween. (i) the preform support including a first member of a first projection/receiver arrangement thereon; the first member including a first projection member (295, 377) including first and second sidewall sections having portions non-parallel and diverging from one another; (ii) the preform support includes a first projection member of a second projection/receiver arrangement thereon; the first projection member of the second projection/receiver arrangement including first and second sidewall sections having portions non-parallel and diverging from one another; (iii) the first projection member of the second projection/receiver arrangement is shaped and positioned as a mirror image of the first projection member (295, 377) of the first projection/receiver arrangement with the media pack positioned therebetween.