A precision liquid pipetting device having an elongated barrel, a pipette tube mounted to one end of the barrel and a plunger assembly carried in part within the barrel and including a plunger tip reciprocable within the pipette tube to draw liquid into and to dispense liquid from the pipette tube, the improvement comprising a finger button removably secured to the plunger assembly on one end and an adjustable stop mounted on said finger button for limiting movement of said plunger assembly and providing precise control of the amount of fluid dispensed from the pipette tube. In addition, a body extension assembly is provided to adapt the pipetting device for connection to a valve body.