On 6/3/2018 10:44 AM, Frank wrote:
I am trying to install a ceiling fan (about 17lb).Â* The outlet box was
plastic
and probably not rated for ceiling fan so I have it knocked out and was
planning to use a ceiling brace kit.Â* However I noticed that the joists was
too close apart and the bar of the brace kit is too long.Â* One joist is
flushed to the edge ofÂ* the hole.Â* I wonder if I can just screw a metal
outlet
box to it.Â* Will that be strong enough as the support is going to be
only on
one side of the outlet box.

Not sure I understand. You want to use one support and then screw the
box directly to the joist on the other side? That can work if you use a
long enough screw. If it is attic above, you may be able to reinforce
from above too.