Red Hot Piston

The Red Hot Piston is an item associated exclusively with adding an effect to weapons crafted through the Forging Interface.

Crafting
The item is crafted using 2 Fireblossoms, 1 Hellstone Bar and 5 Stone Blocks at an Anvil.

Effect
Adding the item to the Effect Slot in the Forging Interface will result in your weapon creating fire particles when swung, and having a chance to [http://terraria.gamepedia.com/On_Fire! light enemies on fire] for 3 seconds.

The formula for calculating the chance is:

60/aps/60, where 'aps' is the attack speed in attacks per second.