[Engine] Allen key size

[Atomic Jack]

Hello folks
               I aim to change the glowplugs on my 53 plate 1.9d but i havnt got a correct size allen key to take off the cover that goes over them...its the larger size key that i need.Could anyone give me the size please,
                                                                                                                                  Thanks in advance,Jack.

[Top drive]

The inlet manifold ?

Those are 6mm

[Atomic Jack]

Its the very deep ones that sit over the head,,,thankyou.