I don't really want to add to the calling out of the guides, but this is from one of the guides:
Ragnarod said:
Concentration – this aura is the only one that enhances the damage from Blessed Hammer, another skill to max. 20 points here
Regarding the Hammerdin.
The only casting break points you should really concern yourself are last and second last - 125% and 75% respectively. There is a lot of debate over which is the best, especially when asked, "which is better, HotO or Wizspike?" HotO will add a lot of damage to your hammers, and you can easily get to the 125% FCR with it...whereas with the Wizspike you can easily get to the 125% FCR but will do less damage. What you do is your personally preference.
As others have stated Concentration adds to the damage of your hammers, but by 50% it states.
Hammerdins can complete Hell on players 8 with a good setup, and when duelling the nice thing is to not use Concentration. Some circles don't allow you to teleport if you have Enigma...but really use Vigor and you'll be fine.
A good setup which is achievable is:
Helm: Shako
Armour: Vipemagi
Weapon: HotO/Wizspike/Suicide Branch
Shield: HoZ
Belt: Arachnid's
Gloves: Frosties/Magefist/Trangs Claw/Crafted/Rare/Chanceguards
Boots: War Travs/Waterwalks etc
Amulet: Telling of the Beads/Mara's/Crafted/Rare/Magic
Rings: SoJ x 2 / SoJ and BK
Charms: Lion Branded Skill charms.