You stuff the wire through the clamp. Insert the wire INTO the box from outside it goes smoothly. If you want to run wife from the box outward, you need to pry the clamp away from the wire a bit.

Ron,

I kind of figured something like that. Of course, this box has a two fingered clamp, kind of a inverted V shape.

The project I'm working on is going to be pretty easy, I just need to pick up power in a box and only go a short distance (maybe 18-24") and install a new box. In a metal box I'd just pop the knock-out and fish one way or the other.

I'm sound (and feeling) like an idiot here but do I pry back the fingers, push a fish out the back, grab it, pull it out the other hole, tie my cable on, and then pull it back?

Yeah it sort of works like those chineese handcuff things. The plastic boxes are great if your'e doing new construction but they're a big pain if you're trying to fish things up from them. If you're using old work boxes I would just fish the wire before installing the box and then CUT it and stuff the cut ends through the clamps.

Old work with NM cable is the same with steel or nonmetallic boxes. The box hole is cut in the wall, the cable fished through the box hole, the box mounted onto the cable and then the box is installed in the wall.

"I'm sound (and feeling) like an idiot here but do I pry back the fingers, push a fish out the back, grab it, pull it out the other hole, tie my cable on, and then pull it back?"

Yes, that would be the easiest route. The holes are made to be one-way from outside to inside. It will be easier pulling cable from the new location into the existing box.

I failed to mention that one should determine as much as is possible that a cable can be fished to the proposed box location BEFORE cutting the box hole, especially if the wall surface is not easy to patch-- such as solid wood paneling. Don't ask me how I know!