Here's the description from
Digital Racer
JIC Coilover Suspensions (SF-1 Mono Ball Rear Upper Mount) - G20 (P10) [1991-1996]
JIC threaded coil over systems with aluminum mono ball upper mounts and progressive springs have higher shock and spring rates designed with bump stops. Twin tube design and using 36mm pistons for strut application. Shocks are rebuildable and revalvable for all application. *** All JIC products are designed for Japanese domestic market vehicles, fitment is not guaranteed on US domestic market vehicles.***
I agree, the springs do look linear, but they feel progressive. I've only had the car for a few weeks, but I'd also like to add that the setup is pretty quiet. Since they're a real coilover, there's removable collar, and no need for the DIY silicone/duct tape remedy.