Distorted Vision coughed up some electrons that declared:

Mine still don't come out too neat. The problem is when I use the
pliers after cutting with a hacksaw it makes a mess of it instead of
leaving a clean straight edge. Maybe a tile scribe and nipper might do
the trick?

Unless you're really unlucky, the pliers should break it off "short", then
you can clean up with a file. I've only found that it over-breaks (chips
the box well beyond the hole area) if you don't use a hacksaw first to
slice the side.

As I mentioned previously, I've found a big (8" ish) square file to be
particulalry quick and effective.

Cheers

Tim