This is a unique sledgehammer with 32 damage; it can do 37 damage when your Melee Weapons skill reaches 100 and its condition is 100%. It can be repaired with normal Super Sledge. In the "Finding The Garden Of Eden" quest, help Fawkes out from his captivity inside Vault 87 and let him get the G.E.C.K. for you, or kill him to obtain this melee weapon.