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, a collar having an upper opening for receiving a pipette tip mounting shaft, the inside surface of the collar including a circumferential locking ring extending inward from an inside surface of the collar, and 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, the barrel of the disposable pipette tip having a sealing area at its upper end; and a pipette mounting shaft including a lower sealing section and an upper locking section, the locking section of the mounting shaft including a stop that engages the shelf of a 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 the locking ring on the inside surface of the collar, and recessed relief portions in the upper locking section of the mounting shaft spanning between the lobes such that the collar distorts outwardly at the lobes and inwardly at the recessed relief portions when the pipette tip is locked on the mounting shaft over the stop and the lobes wherein the lower sealing section of the mounting shaft seals against the sealing area at the upper end of the barrel of the pipette tip when the mounting shaft is fully inserted into the collar of 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, a collar having an upper opening for receiving a pipette tip mounting shaft, the inside surface of the collar including a circumferential locking ring extending inward from an inside surface of the collar, and 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, the barrel of the disposable pipette tip having a sealing area at its upper end; and a pipette mounting shaft including a lower sealing section and an upper locking section, the locking section of the mounting shaft including a stop that engages the shelf of a 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 the locking ring on the inside surface of the collar, and recessed relief portions in the upper locking section of the mounting shaft spanning between the lobes such that the collar distorts outwardly at the lobes and inwardly at the recessed relief portions when the pipette tip is locked on the mounting shaft over the stop and the lobes wherein the lower sealing section of the mounting shaft seals against the sealing area at the upper end of the barrel of the pipette tip when the mounting shaft is fully inserted into the collar of the pipette tip.