Product review (5 stars): LOOK FOR THE ARROWS
There are raised arrows on the end pieces.  If you turn them in the direction of the arrows they pop right onto the vent if you follow the directions on the bag.  I don't quite understand why the ends couldn't have been installed at the factory, through -- it should be easy enough to get one off if the length needs to be adjusted.  THIS WAS JUST ABOUT THE EASIEST THING I'VE EVER INSTALLED ON ANYTHING!

Once assembled, the vent pops right onto the required places, and stays put.  Now I can FINALLY clean the duct without the trauma of having to make the duct go directly onto the fittings -- and no more of those [expletive deleted] screw-on harnesses!

Your mileage may vary, but this is one of the most useful items I've bought recently.