106 responds to the deflection force established in lever portion 100 to return toward symmetry with axis 103 to a position in which blocking section 108 is in a substantially abutting relation with top wall 70 blocking section 108 resists removal of latching portion 102 back along the installation path indicated by arrow 105 without first deflecting latching portion 102 from axis 103 joining structures 20 22 24 26 fig1 may thus be established preferably in combination by insertion of insertion structures 82 within receiver structures 56 and by insertion of latching insertion structures 84 within stop structures 58 it is preferred that receiver structures 56 stop structures 58 insertion structures 82 and latching insertion structures 84 each be integrally formed with a respective first member 12 14 or a respective second member 16 18 as appropriate to establish joint structures 20 22 24 26 substantially rigidly about respective axes 30 32 34 36 fig1 while any polygonal structure may be established circumscribing volume 40 fig1 using the teachings of the present invention a preferred polygonal shape is a quadrilateral shape and especially a rectangular shape maintaining a predetermined polygonal shape for a filter element contributes to reduced air leakage around the filter element when it installed in an air duct or other installation site fig1 is a flow chart illustrating an embodiment of the method of the invention in fig1 a method 200 for providing a frame for receiving a filter element begins at a start locus 202 method 200 continues.