its a plate that welds to the spring mounting area and has a large bolt through the center.. then a cup of sorts that screws down onto the bolt.. which lets you adjust your amount of lift from 0-2.5" or 2.5-5" i think
For the most part that is correct, except the welding the plate. I just set mine in there and also added an additional polyurethane "donut" to cut down on any metal on metal. The VX has one of these "donuts" on it from the factory, but it is made out of rubber. It goes in between the top of the spring and the upper spring perch. If you do some really crazy offroad stuff where you really articulate your rear end to where the springs could possibly fall out, then you may want to anchor those plates in there somehow. When I did my lift though, I found that between the spring tension and the shock travel I really doubt they could fall out with the additional 4.5" in there. The shocks just wont travel enough to allow it to come loose, although for ~1" lift they obviously would. Another point of concern is that the last time I checked, they(speedway) was only offering one of the two sizes of spring jacks. The Easiest way to add an inch though(by far) is just to throw in a set of 1" poly spacers and call it a day. Although it is more spendy. You could lift it in under an hour this way-super easy.