Engineer's Blueprint

The Engineers Blueprint [sic] is an item added by Immersive Engineering. It is used in the Engineer's Workbench: putting it in the main slot of it will the crafting of special items. Different blueprints exist for the creation of different items.

Common Projectiles
The Common Projectiles design can also be obtained by trading with the Engineer Villager, for 2 Emeralds.

The Common Projectiles design is used to create Casull Cartridges, Armor-Piercing Cartridges, Buckshot Cartridges and High-Explosive Cartridges.

Specialized Projectiles
The Specialized Projectiles design is obtained by trading with the Engineer Villager for 7 Emeralds. It is used to create Dragon's Breath Cartridges, Homing Cartridges and Wolfpack Cartridges.

Arc Furnace Electrodes
The Arc Furnace Electrodes design is obtained by trading with the Engineer Villager for 18 Emeralds. It is used to create the Graphite Electrode.