Scratch File Set

Tells you how hard an edge or a plate is, by which file bites it.

Crafting

Shapeless: an Iron Ingot, Flint, a Nether Quartz and Leather.

Using it

Carry it anywhere in your inventory. A modular item's tooltip gains a line like "Scratch files: scratched by file 5, not by file 4".

The set has eight files, each harder than the last. A file scratches anything softer than itself, so the reading is a rung, not a number: your edge is harder than file 4 and softer than file 5. A set of files can't honestly say more than that.

Hardness decides what a tool can dig (see Tools and Weapons) and how hard a plate is to pierce. Materials lists the numbers if you'd rather look them up than measure.