With standard serological pipettes, there has never been a difference in the plug end design. All require high insertion force (jamming) in an attempt to get the top as high up in the pipette controller nozzle as possible. You do this to try to get as much stability as possible otherwise, you risk dripping of the liquid you pipette. No matter how hard you jam, there is wobble.
Wobble-not serological pipettes are a revolutionary, new design and the only serological pipettes that will give you two zones of contact with relatively low insertion force. No jamming! And furthermore, this results in maximum stability for your pipetting. No other serological pipette comes close to achieving the same amount of Wobble-not!