There are 2 items that are called "Iron Hammer" in ECO. They should have named them uniquely to avoid confusion for players.
The first "Iron Hammer" can be used as a Tool and also synthesis Material. Lucky for you it's sold in most Jewelry Shops for 1,000 gold only. So you can get as much as you need or ever want as long as you got the gold.
http://onlinegame.guide101.net/wiki/Emil_Chronicle_Online:Iron_Hammer
And, the other "Iron Hammer" can only be used as synthesis material for making Mace Weapons or an Iron Bullion synthesis material.
http://onlinegame.guide101.net/wiki/Emil_Chronicle_Online:Iron_Hammer_(1)
This 2nd "Iron Hammer" can be found inside Treasure Chests or only be made through synthesis using the first "Iron Hammer" tool as the synthesis material.
The wiki links I gave gives the correct recipe. Some other wiki have this 2 "Iron Hammer" items mixed up on their synthesis recipes, therefore having the wrong recipe for all items that has Iron Hammer as tool or synthesis material. However, I won't say which one. Can only blame game translators for negligence, they should have given these two different items a unique name to avoid confusion.
Same problem goes with Needles. There are 2 items called "Needle" in the game. And a lot of items use needles as tool and material. Causing some English wikis to also have the wrong recipe information for some items.