When I replaced the GFCI in one of my exterior receptacles, I found that the installer had simply drilled a 3/4" hole through the house's wall and fed the cable through it and through the threaded opening in the back of the electrical box:

What should I use to secure the cable where it enters the electrical box? I'll be re-applying caulk around the electrical box when I'm done; is there anything else I need to do to seal the hole in the wall (3/4" seems excessive for a single 12/2 cable)?
