2016 CX-5 hatch rattle; nut size needed

[txt990]

My 2016 CX-5 sport has been making a rattling sound in the rear. As it turns out when you lift the hatch, the right nut is missing. I guess this nut holds the spoiler. On the left side it was loose and I tightened it. What is the part # or type of nut that I can use?

 

[N7turbo]

I would take the other one to the hardware store and match it up.