These are 5 pieces reducing straight 1/4" Tube OD x 1/4" 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 1/4'' in outer diameter, used to fit 1/4'' 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..