Blaze Rod is an item added by vanilla Minecraft.
Blaze rods are Standard Vanilla Items, dropped by Blazes or found in Loot chests. Blazes are commonly found in Nether fortresses, but also appear in Battle Towers.
In Hexxit Blaze Rods have the following Purposes:
"Fiery" Modification of the Tinkers Construct Mod: Blaze Powder, obtained from putting Blaze rods into the crafting table, is put into the Tool Station together with a weapon of choice (applies to Tinkers Construct Weapons or Tools only) to add the "Fiery" Modification. This Modification can stack up to 25 Blaze Powder onto the Weapon. The modification enables fire damage upon hitting a mob with the weapon or tool (similar to the Fire Aspect enchantment). The duration of the fire is dependent upon the amount of Blaze Powder applied to the weapon. NOTE: This Modification is most effective on weapons, but also works on any tool.