A disposable pipette tip having that is configured to mount on a tip mounting shaft having a locking section and a separate sealing section. The locking section has outwardly extending locking lobes circumferentially spaced around the mounting shaft and located above a stop member that separates the lower sealing section from the upper locking section. The collar flexes out of round when it is mounted over the locking lobes on the mounting shaft. The circumferential shelf on the tip isolates the tip barrel from distortion to enable robust sealing in the barrel below the shelf.