Leaf spring hangers are basically exactly that, they are brackets that are either welded, bolted or riveted to the side of a truck, SUV or car chassis to support the leaf spring of in most cases is a straight axle.
Accompanied by the front and rear hanger is a shackle. The shackles main intention is to keep the leaf spring from putting unnecessary tension on the hangers. This is done by allowing the shackle to pivot from the hanger and leaf pack and allow bound tension to move side to side with the articulation of the shackle. The longer the shackle the more movement the leaf pack can make before binding, if that makes sense. Shackles can also be longer or shorter depending on the position and if you are looking for lift or drop, but we can get into that in a later post.
When installing aftermarket lift or drop hangers, traditionally this part gets installed in the forward hanger position (closest to the cab of the truck). This is because if installed into he rear you may run into clearance issues (especially when doing a drop) depending on the shackle length. This also suggests that we should just modify the shackle instead of replacing the whole hanger. So this is why the industry standard when installing lift or drops on leaf spring suspension is to replace the rear shackle and front hanger unless the part is structurally unstable in which case an OEM replacement would be necessary.
For a complete rundown of hangers available for many import and domestics check out the link below: