These are simple yet effective TJ, or LJ rear coil spring retainers. They are sold as a set of 4 with lower hardware. Simply drill and tap the lower coil bucket and sandwich the 4 inch round plate on top of the coil. And install another disk on the top of the coil between the bumpstop cup and the coil spring. And you wont have to worry about your coils ever falling out again.
Sold as a kit.
Note: Drilling and tapping a hole in the lower coil bucket is required.