Soft and Hard Arkansas are grade names makers give natural novaculite stones, and on Case's pages the soft grade is the coarser one. Case's kit pages call Soft Arkansas both "medium" and "a coarse stone" and call Hard Arkansas "a finer stone" used to refine the edge. Buck's 2026 catalog also labels its own Soft Arkansas stone coarse, spelled "Course".
Soft and Hard sit on one rock: Case calls its Hard Arkansas pocket stone novaculite, and Buck's 2026 catalog gives novaculite as its Soft Arkansas stone's material. The Arkansas Geological Survey calls novaculite, the rock behind the name Arkansas stone, "a recrystallized variety of chert". It says the abrasives industry classifies the rock into two categories: "Arkansas" stone ("extremely fine-grained") and "Washita" stone ("less dense, more porous").
The survey's page names no Soft, Hard, Black or True Hard grade, so its two categories and a maker's grade name are separate labels.
Soft Arkansas
Hard Arkansas
Black Arkansas
True Hard Arkansas
Case's Sportsman's Honing Kit page calls coarse stones "the foundation stones of any sharpening kit" and says "Using a coarse stone is the fastest way to get a good shape on an edge", with the hard Arkansas used to refine that edge. Buck's how-to page runs the same way in three stages: a coarse grit sharpener for nicks or extremely dull blades, a medium grit sharpener for touch-ups and final sharpening, then natural stone or a fine grit sharpener.
Whether one stone can do the whole job is taken up under needing different grits for sharpening; the method belongs to how to sharpen a pocket knife.
Case's website describes Tri-Hone model 09399, while its 2026 Product Guide lists Tri-Hone model 50305 with different stones. Those are different model numbers. The EZ-Hone documents also list different stones under model 09398. Check the model and the box or insert before applying a kit description to the stones you own.