You insert it from the bottom of the clip, the part that will be inside the box. Leave it extend above the clip about 1/2". Now, push the clip down over the side of the box (with whatever will work), bend the 1/2" tail over the side of the box and trim it off if necessary.
That said, these things are a big PITA! I rarely use them and, as said, will only work on a straight sided box.
-Hal
[This message has been edited by hbiss (edited 04-07-2004).]
