a pipette assembly for automatic pipetting machines including a stepped mandrel and tip for providing a minimum contact seal between the pipette tip and mandrel . the mandrel includes a first cylindrical portion with a first exterior diameter and a second cylindrical portion with a second exterior diameter . raised bands on the first and second cylindrical portions contact the interior wall of the pipette tip to form seals . because only a portion of the mandrel , specifically the seal portions , contacts the pipette tip , lower forces are required to insert the tip onto the mandrel .