hillerup
There are basses, and there are Thunderbirds!
I tried two of them but they wouldn't screw down very far so I was extra careful not to force it.
Maybe you accidentally tried the two metric screws - Try using the other two...
The difference between metric and imperial screws is very subtle, but significant enough to make a difference.
Either that or you've just been unlucky and gotten 4 metric ones in the box...