equipment grounding screw size

[Smiley64]

I am replacing 80 light fixtures on a cement ceiling that has PVC conduit connected to a plastic box then a metal octagon extender over the plastic box to bring it flush with the surface. The extender has an 8-32 tapped hole in the bottom tab. I can't find what size the grounding screw has to be in the NEC. Does it have to be a #10? Does the grounding wire from the extender into the fixture have to be #12 if this is a 20A breaker? (250.122)

 

[Dennis Alwon]

250.8 (A)(5) will give guidance. 8/32 should be fine

 

[infinity]

Why not use a PVC box extender?

 

[Smiley64]

The existing extender is in the cement already, it can't be removed.

 

[ptonsparky]

Yes the EG should be at least 12. What size wires were pulled?