Agri-Pro© Pritchard Flutter Valves were invented in 1979 by Jack Pritchard and feature a unique hollow cone design that allows adjustable feeding rates. The valve admits air while preventing milk from squirting out the vent, ensuring no mess or waste, and the nipple cannot be pulled from the bottle. The Veri-speed nipple can be easily trimmed with scissors to adjust flow, making it suitable for both strong and weaker lambs. It screws onto most bottle sizes, including 2-liter plastic bottles, for convenient use.