proberly one of the cheapest mod you could do, if your bottoming out or wanted to stiffin up your shocks, i got them done because mines a bit lower as well as bump stops... its just a bottle cap off a drink bottle comes in any colour lol they work a treat because the spring sits nicely on the thread and does not go all the way through, have got black metal wine bottle ones on the back but their a bit harder to see with my shitty camera