What’s the spanner called for these “four side notch” collars/bolts

Usually, around the home anyway, there are other signs to let you know when you've applied enough torque. MarkD noted a common one -- when you see the screw head just go below the surface of the wood. In your fencing example, if you're tightening lag screws or nuts with washers, you'll see the washer start to sink into the wood long before you've applied enough torque to shear off or strip the screw or bolt.

It's a great tool for this kind of work, and it's super fast. Don't slow yourself down unnecessarily by underestimating your own ability to judge how much torque you've applied, and how much is enough for your application.

Two things unbelievable about my answer.

1. It's not about electrical
2. I took pictures of my toilet

I think I have the same seat, so here we go...

Excuse the glare, but this is what holds my seat down.

Now take the top half of the clips and twist them counter-clockwise. The picture shows them all the way turned. Now the hard part...

You might have to work at this but you give it some wiggles and it pulls straight up.

Hopefully this is what you have and hopefully the artistic work I did does not go in vain. Taking pictures of toilets or loo's or any device of this nature just does not do anything for me. I hope they don't pull my man card, then I have to get my you know whats out of my wife's purse.