If you're looking to lower the rear height of you Chevrolet Silverado or GMC Sierra 1500 pick-up truck than these are for you. Essentially, what these shackles do is go between the rear leaf-spring and the frame, creating a shorter distance between the truck and the ground. These shackles will lower the truck up to 2". The product isn't badly priced either. Note: If you're looking to lower both the front end and the back end of your truck, you will either need to have a 4WD truck, or if your truck is 2WD you will need to buy additional parts to lower the front. Even with the very limited installation instructions, the installation was a breeze. If you know what you are doing this is a one man job that will take less than an hour. If you don't have a clue about what you are doing it is a two man job that will take around an hour as well. So a very quick and painless installation is a nice feature.