Thread size for the + Power Block 2015 - 1500 and Bed ground location

[Doghouse]

I am looking to install an inverter in the bed of my truck, and found the Power block for the positive terminal and was psyched to see an empty terminal. Since then I have been trying to find out what the thread size is for the studs.

 

Secondly I am looking for recomendations for the Neg. Ground. My plan is to come though the plastic plug above the wheel well and attach the 1kw inverter there.

 

Thanks for the suggestions and advice. My dogs need to keep cool!

[Doghouse]

Went to the hardware store and borrowed their gages. It is an M8 1.25 stud.