A pipette tip and mounting shaft combination in an air displacement pipette, the combination comprising a pipette tip mounting shaft having a radially stepped exterior comprising adjacent substantially cylindrical portions of different diameter and an annular sealing zone including an annular edge seal at an outermost edge of a radially extending shaft transition, a pipette tip including an annular sealing region having an inner sealing surface on a sidewall of the tip which in the sealing region is sufficiently thin as to expand slightly and form an interference fit and air tight seal between the sealing surface and the sealing zone when the sealing zone penetrates the sealing region, and axial penetration limiting means for limiting penetration of the shaft into the tip to limit axial contact between the sealing region and the sealing zone to a narrow annular band comprising the annular edge seal.