I use the 5/8 threaded rod they have a Home Depot. Just the regular stuff. The tensil strength of the rod is twice what it will take during compression. Be careful not to damage the threads.
To compress I use a piece of 1/4 to 1/2 inch flat stock on the bottom and double washers on the top. I also double nut the top. I disconnect the lower control arm so it doesn't interfere in any way. I detach it at the ball joint while there is some spring pressure and I detach it at the bushing after I have let some spring pressure off.