Identifying lock shield side of radiator

[MarkToday]

I am trying to balance my central heating. My radiator in the hallway is in the photos below. Is the lock shield the one with a small metal disc in the middle. If so do I have to pope the disc off. It spins freely but doesn't seem to want to pop.

 

[denso13]

The one on the right, it should either be fixed by a screw in the middle or it will just pull off.

 

[MarkToday]

Thanks. I was entirely sure which was which. It has a metal cap on the middle. I assume this will pop pop off - although it doesn’t seem to want to

 

[Rodders53]

Looks to be an anti-tamper / security screw holding both valve heads in place... which may make removal a slight challenge.

Security bit sets are available from diy shops (inc amazon/eBay) or needle nosed pliers can sometimes be used to undo them (damaging the pliers often though).

They look to be "Spanner drilled" type or maybe spanner slotted... https://marshfasteners.com/tamper-proof-fasteners/#post/0

 

[denso13]

I assume this will pop pop off - although it doesn’t seem to want to

It should turn, as above get the correct bit, or try and knock it round with a screwdriver against the small slot. It "should" turn easily enough, just small screws.

 

[Madrab]

Is the lock shield the one with a small metal disc in the middle.

Technically both could be the lockshield, as both are manual valves. It just comes down to which one has the blind cap, i.e. the smooth cap that isn't designed to turn by hand.
If you are the only one that would actually work the valves though then you could just use the turn valve on the left and mark it with how many turns it's to be set to.