A pipetting system comprising: a disposable pipette tip having: a barrel with a lower opening through which liquid is aspirated into the barrel and dispensed from the barrel, the barrel having a sealing area at an upper end of the barrel, a collar having an upper opening for receiving a pipette mounting shaft, the lower end of the collar having a larger inside diameter than the inside diameter at the upper end of the barrel, and a circumferential shelf that connects the lower end of the collar to the upper end of the barrel; and a pipette mounting shaft including: a lower section, and an upper locking section, the locking section of the mounting shaft including a stop that engages the circumferential shelf of the pipette tip when the mounting shaft is fully inserted into the collar of the pipette tip, two or more outwardly extending lobes spaced equally around the locking section of the mounting shaft and located above the stop on the mounting shaft for engaging an inside surface of the collar, and relief recessed portions in the upper locking section of the mounting shaft and spanning between the lobes such that the collar distorts outwardly at the lobes and inwardly at the relief portions when the pipette tip is fully mounted on the mounting shaft; wherein the lower section includes an annular groove with a sealing ring located in the annular groove, and wherein the sealing ring engages the sealing area at the upper end of the barrel of the disposable pipette tip when the mounting shaft is fully inserted into the pipette tip. a disposable pipette tip having: a barrel with a lower opening through which liquid is aspirated into the barrel and dispensed from the barrel, the barrel having a sealing area at an upper end of the barrel, a collar having an upper opening for receiving a pipette mounting shaft, the lower end of the collar having a larger inside diameter than the inside diameter at the upper end of the barrel, and a circumferential shelf that connects the lower end of the collar to the upper end of the barrel; and a barrel with a lower opening through which liquid is aspirated into the barrel and dispensed from the barrel, the barrel having a sealing area at an upper end of the barrel, a collar having an upper opening for receiving a pipette mounting shaft, the lower end of the collar having a larger inside diameter than the inside diameter at the upper end of the barrel, and a circumferential shelf that connects the lower end of the collar to the upper end of the barrel; and a pipette mounting shaft including: a lower section, and an upper locking section, the locking section of the mounting shaft including a stop that engages the circumferential shelf of the pipette tip when the mounting shaft is fully inserted into the collar of the pipette tip, two or more outwardly extending lobes spaced equally around the locking section of the mounting shaft and located above the stop on the mounting shaft for engaging an inside surface of the collar, and relief recessed portions in the upper locking section of the mounting shaft and spanning between the lobes such that the collar distorts outwardly at the lobes and inwardly at the relief portions when the pipette tip is fully mounted on the mounting shaft; a lower section, and an upper locking section, the locking section of the mounting shaft including a stop that engages the circumferential shelf of the pipette tip when the mounting shaft is fully inserted into the collar of the pipette tip, two or more outwardly extending lobes spaced equally around the locking section of the mounting shaft and located above the stop on the mounting shaft for engaging an inside surface of the collar, and relief recessed portions in the upper locking section of the mounting shaft and spanning between the lobes such that the collar distorts outwardly at the lobes and inwardly at the relief portions when the pipette tip is fully mounted on the mounting shaft;