A packer tool having simple and reliable setting and release systems comprising three or more slips evenly distributed around a mandrel. Each slip comprises two members with gripping teeth which, except for one slip, typically have the capacity to grip a well casing in opposite axial directions. The remaining slip has only one member with teeth able to grip the casing, the other slip member has dummy teeth with nil gripping capacity. The latter teeth have blunt or rounded edges and are not slanted in a selective gripping direction as the sharper teeth of the other slip members.