How to tighten bolt?

[Burnerman]

You need to hold the smooth round head, correct? In which case it's mole grips or slip joint pliers to get a good grip......you just need to stop it spinning whilst you try to move that Nyloc nut.
I'd still replace that bolt for ease in the future.
John

 

[JohnD]

quite right

I was thinking of the nut

 

[joe-90]

Have you tried one of those split ring type washers under the nut? They often exert enough force to stop the other part from spinning whilst you tighten it.

 

[SmoothCriminal]

Have you tried one of those split ring type washers under the nut? They often exert enough force to stop the other part from spinning whilst you tighten it.

Indeed, it is not visible in the image but there is one under the nut.

 

[333rocky333]

Retry with the washer under the head rather than the nut.
Or is the bolt in the pic another one and the problem one still fitted and wont move either way.

 

[bernardgreen]

Cut a slot across the head of the bolt with a hack saw and use a flat bladed screw driver to prevent the head turning.

REMOVE THE MONITOR FIRST to prevent metal filings getting into the monitor.

 

[SmoothCriminal]

Finally managed to remove the bolt and the screw. The edges of the bolt were nearly worn down (the whole set is not best quality). In the end it took an adjustable wrench holding the screw on one end and a bigger wrench turning the bolt...

I will replace the screw with one with a square or a hexagon... the current screw is 7mm in diameter, I understand this is an m7 screw?

*Edit: this is peculiar, I can't find many M7 screws online.

 

[mattylad]

More likely an M8 bolt...

 

[magicmushroom666]

The underside of that smooth round head is square, which is designed to fit into a square hole in the bracket (assuming its the original bolt) In the first photo it looks like the bolt is the wrong way around, ie the washer is underneath the bolt head rather than the nut. I'd check the bracket etc carefully for the square hole. It's much easier fitting something like this when one side is held rather than using a normal bolt and having to hold it from both sides.

 

[JohnD]

if you do still have a square hole, look for a coach bolt.

 

[SmoothCriminal]

The underside of that smooth round head is square, which is designed to fit into a square hole in the bracket (assuming its the original bolt) In the first photo it looks like the bolt is the wrong way around, ie the washer is underneath the bolt head rather than the nut. I'd check the bracket etc carefully for the square hole. It's much easier fitting something like this when one side is held rather than using a normal bolt and having to hold it from both sides.

Turns out this was the problem all along. I removed the washer under the bolt and put it under the nut. Then I could tighten the nut as far as it could go.