how to remove this ?

hi , whats this called ? & how do i remove it (make a tool ?) to replace shock 
 

 
cheers

Gland nut.  It may be easier to buy the correct tool or borrow one if you don't do strut inserts very often. Vice grips work as suggested above but sometimes the gland nut is done up very deep and you cant get vice grips onto it.
Cheers

Before you go to the trouble of finding/making a tool, see if you can get it out with a screw driver and small hammer.  You should be able to tap it around.  If not, take your struts to a suspension shop and ask them to undo it for you.

"gland nut".
Cannot be called a gland nut because it does not have a gland or seal, and the nut does not prevent the loss of liquid from a valve. The nut simply retains the damper insert inside the strut.

I use a pipe wrench if can't move it with a hammer and blunt screwdriver. Also lightly the thread area with hammer before attempting to undo the retainer/gland nut .

Whatever you want to call it Ive learnt that its a nut that can come loose in service so either use locktight or once its done up use a punch to deform the top edge of the tube, dont go over board as you might want to undo it again sometime.
Another tip is before its put on fill the gap between the insert and the strut tube to about 50mm from the top with oil. The theory here is that if an air gap is left it will impede the heat transfer to the outside of the strut causing shocker fade and shortened life. ( the shockers life and possibly yours too).

"so if you reused it to retain your new inserts it would still be called a Gland nut."
 
Absolutely correct the original Ford item was a gland nut. And the diagram supplied is correct.
However the photo 70 Capri supplied is a nut supplied by an after market shock absorber company to use with a sealed damper and has no seal or gland. So it is just a nut.

For heat transfer the k value for air is 0.024, oil 0.15, water 0.58 so antifreeze would be better than oil but would you trust it corrosions wise?  But for street use do we need to even bother with oil?  No doubt it would be better but is it necessary or a bit of over kill?  
 
I have seen some with a small tack weld on the nut to hold it in place.  Dont forget to put the spacers in the bottom otherwise the insert will rattle no matter how tight the nut is.
 
For the nut name debate the original strut was oil filled with its own piston setup so it was truely a gland nut with an O ring fitted.  Cartridge style inserts are after market and were made to suit the original setup and tooling but I think they call them the retaining nut.  In some shops today the young fella serving you will give you a blank stare no matter what you call it