These are 3 pieces reducing straight 1/4" Tube OD x 3/8" Stem OD Quick Connect RO Fittings, widely used for installing a refrigerator line that has to go some distance, or fridge/ coffee maker, leak free, the stem is 3/8'' in outer diameter, used to fit 3/8'' push to connect fitting, the other side is used to fit 1/4'' ro water line. Different styles and sizes of fitting and water tubing are all available to choose in store..