If this box doesn't have internal screws to attach it to the bar above, it's
not a bar box. It would likely be a side bracket box, nailed to the side of
a ceiling beam. The best thing to do is completely remove the box and
install a fan support box. There are ones like Westinghouse 01100 which will
install from below and bridge the beams. If you can get above the box to
install support wood, you should be able to easily remove the existing box.
If you did choose to use the existing box with wood support above it, Don't
support the fan from the plastic threads, but run long lags through the box
and into the support wood above



"Apropos" wrote in message
...
I wish to hang a clg fan where there's an existing plastic box.

I believe the plastic box is supported by a metal between-stud bracket. I
plan to reinforce the box by putting a 2x4 above the box and using lag
bolts
w/washers thru the box to support it.

My question would be the THREADS of the box. I'm sure the box itself, as
it
will be supported, would well stand the force of the fan; however there's
a
big question if the THREADS would have any problem.

One thing about the plastic threads is that you have a large number of
them
(sticking the screw up to 1" into threads) as opposed to the steel, which
has only a small number of threads. Anyone have experience with this?

If I need to get the box off, how best to do that? Would I *HAVE* to do
it
in the attic? It's VERY hard to get in there and I want to use the
existing
hanger, only REINFORCING the box with the new wood. I don't see any
internal screws which hang the fixture