Materials used to craft a Upgrade Kit is different depending on which kit. The first kit (wood to stone) uses 1 cobblestone, 2 planks, 1 string and 1 flint, where the latter uses 1 of the previous material and 2 of the latter + the previous material's upgrade kit.
When put in the workbench with an item that matches the material tier (eg. wood, stone, iron, gold etc.), the player can upgrade the selected tool to a higher tier.
- Before AbyssalCraft 1.5.5 (I think), enchantments wouldn't persist when using an upgrade kit. They do now.