Designed for use with conventional coil springs with a mono-ball and stud to eliminate any binding between the spring cup and jack bolt. The stud threads into jack bolts with an internal thread (Allstar ALL56090). Two styles available: Welded Style, where spring sleeve is welded to the plate, or Pro-Series which incorporates a bolt-on spring sleeve. The Pro-Series allows proper fit to varying coil spring diameters and rates.