Stun Vials are items obtainable in the Clockworks from monsters or crates. Stun Vials stack to 3. Stun Vials cannot be taken out of the Clockworks.
A Stun Vial is a throwing item used to inflict the status ailment known as Stun. When thrown, the vial will burst on impact with a monster or a wall.
To throw a Stun Vial, select it from the top of you HUD by either clicking it, or hitting the number it is assigned to (1, 2, 3, 4). Once selected, your Spiral Knight will hold the vial over his/her head and hitting the action button will throw it in the direction he/she is facing, instead of attacking with the selected Sword/Gun/Bomb. (If you have the default layout, the action button is Z, or Right Mouse Button) Stun Vials have no charge attack.