I can't take the Dirt Devil Kone filter to fit!? I have the correct, frank Dirt Devil F17 filter and the darn...

I have the correct, frank Dirt Devil F17 filter and the darn thing WILL NOT fit into the gray ring (filter adaptor). What the heck? Anyone own some advice? I've broken 2 filter already!
I just now bought a full-size table made...
Answers:    Do you not have a encyclopaedia to refer to? It's been so long since I owned a Dirt Devil, that I can't remember how to variation the filter. Sorry!