Im assuming you mean to use them so that you can hold the top of the strut with an allen key through the ring spanner. Most of the rear struts I have seen have a flat or somesuch that you can hold without geting in the way of undoing the nuts with a normal spanner. You can buy sockets that can be held by a spanner that I tend to use for the front struts. If you havent done the job before, make sure you have something to undo and re-do the silly castelated nut.