Mace Specialization is a passive human racial ability. It grants an expertise bonus while using mace-class weapons. When dual wielding different types of weapons, Mace Specialization is applied to each weapon individually, so that if you dual wield a mace and an axe, only attacks made with the mace benefit from Mace Specialization. When dual wielding two maces, all of your attacks will benefit from Mace Specialization. For attacks that only use the mainhand weapon, such as a rogue's Sinister Strike, only your mainhand expertise matters.