Solar panel/module grounding bolt size?

[LionKing]

Jinko solar panel has a 4mm hole in its frame for grounding wire connection. Which size bolt should i use for it? M4 or M3? I read somewhere that M4 means 4mm is hole size and bolt diameter is smaller than 4mm, other sites say that M4 bolt means 4mm diameter and it requires a 4.3+ mm hole size. Can anyone confirm which one is true?

 

[chrisski]

I use a nut bolt thread gauge and see which one will fit

Amazon.com

 

[DougfromdaUP]

An M4 screw is 4mm in diameter, and the standard clearance would need a 4.8mm hole. But through a thin aluminum panel I think you could easily get a screw through a 4mm hole. A little screwing action, or tappy-tap-tap.

edited to add: most screws are a few thousandths smaller than nominal, too.