My contractor has installed what he claims is a ceiling fan rated mount in the bedroom of my addition. I went into the attic and it is mounted to a rafter. It seems to be well mounted.

My problem is that it did not come with any screws to mount the ceiling fan to it. I do not know what screws to use in it or if this is a good box to actually have.

The box is plastic. Many other forums say to never use plastic. There is a metal bracket that mounts the plastic box to the rafter.

It appears that a #8 or #10 screw would do. Anyone seen this type of mount before?

The only plastic fan boxes I have seen have had studs sticking down they supplied lock nuts.

The screws from the fan bracket bypass the plastic box and screw into threads in the metal bracket. Metal to metal. Never mount a fan to plastic.