i've used a screw and nut to hold tweeters in stock location but you have to make sure that you have enough roon using the mounting cup for the tweeter to fit behind the door panel...i also had to cut the srew off after i put the nut on because it was too long....
currently my tweeters are stuck to the metal via their magnets then glued into place....they survived a U.P. winter and a couple warm days this summer with no problems yet!