The pipet filler is made of natural rubber,and has three valves that each containing a chemical-resistant stainless steel ball. It's efficient for one-handed operation meet your needs perfectly well,such as control air evacuation, uptake and dispense liquids etc. Sizes of pipet bulb:5.4cm(2.1'') in diameter, 13cm(5.1'') in total length. Accommodates pipettes up to 50ml.