Suspension & Brakes - How long should springs last?

One of my friends gave me his H&R lowering springs that he had sitting around, they have about 50,000 miles on them. Are they even worth my time putting on? Or are they about all used up? Also it only came with one of the fitting deals for the springs. I assume one got lost. Are they only for the front or do I need them for the back also? Can I use the stock ones from my car?

Picture of the fitting deal, since I'm not sure what it is called.

http://www.yourimg.com/?page=05/68/23/MVC009F.jpg

Thanks,
Nathan

anyone?

That goes on the front strut where the front spring will sit on the perch. That one is for the front and should be hard plastic. They will be needed for both sides on the front. The rears are a thick rubber insulator that only goes on the top of the springs in the back. You won't put anything on the bottom of the rear springs. And yes you can use the ones that are on the car right now as long as they are not damaged. As far as how many miles the springs are good for I don't know, but those look like they are in good shape so I would put them on. Hope that helps.