How do you get a windshield wiper to lock on the arm?

I need to change my windshield wipers and I just purchased some replacements. The type I have on my car is a J hook (or some call a U hook) so it should be the easiest kind. I was able to get the old wipers off, and put the new ones on and they fit fine, but they won%26#039;t snap and lock into place, so I am sure they will come flying off. Is there some trick to getting them to lock. I can%26#039;t even seem to see a locking mechanism on the wipers.|||Take the clip off the old wipers that went on the arm and put it on the new one.|||ive had this preoblem and the wipers they say will work for my vehicle dont work so i go to napa auto parts and theirs always work for me