Governance hat: This hat carries legal authority to govern. It is worn when the board member is attend a board meeting. In this role, board decisions are made. The CEO is accountable onl to governing policies set by the board.
Volunteer hat: Carries no legal authority. This hat is worn outside of meetings. Boardmembers then help staffmembers or volunteer themselves, functioning as a resource to the CEO, providing expertise, helping out.
Implementer hat: Similar to volunteer hat, the board member wears this, when he is carrying out a specific task that the board has authorized him to do. E.g. when a board member has been appointed, by board resolution, to be in charge of fundraising, because there is noone else to do it.
Limited authority, seldom worn in most boards.