casing at least one displacement equipment arranged in the lower part of the casing with a displacement chamber at least one seat for detachably holding a pipette point arranged on the lower part of the casing and being connected with the displacement chamber via a channel a spigot arranged on the lower part of the casing to be inserted into the spigot receiver at least one snap hook arranged on the spigot with a claw for engaging into the claw receiver when the spigot is inserted into the spigot receiver and a springy shaft which is deflectable transversely to the axis of the spigot in order to lift off the claw out of the claw receiver a lock release ring movable on the spigot a wedge gear on the shaft and the lock release ring effecting deflection of the snap hook towards the axis upon displacement of the lock release ring in a certain direction and away from the axis upon displacement of the lock release ring in the direction opposite thereto and a coupling equipment for coupling the drive element and the displacement equipment when the spigot is inserted into the spigot receiver application_number US 50808406 A description while this invention may be embodied in many different forms there are described in detail herein a specific preferred embodiment of the invention this description is an exemplification of the principles of the invention and is not intended to limit the invention to the particular embodiment illustrated in the following description the.