On Sun, 03 Jun 2018 20:43:21 -0400, Clare Snyder
wrote:

I am trying to install a ceiling fan (about 17lb). 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. However I noticed that the joists was
too close apart and the bar of the brace kit is too long. One joist is
flushed to the edge of the hole. I wonder if I can just screw a metal outlet
box to it. Will that be strong enough as the support is going to be only on
one side of the outlet box.

Use construction adhesive to add a block to the side of the joist and
screw the box to the joist and the added block

Or just run the support bar between the joists at an angle allowing
the support to fit between the joists????

Be neat to see a photo. Reading the post, my first thought was can
the threaded rod on the fan support box be shortened to fit the space.

I've cut screws to shorten them -- works when done correctly.