When decorating cakes or cookies with a pastry bag, use this coupler to change decorating tips from the outside. Then you can use the same color icing with many different tips. The white plastic coupler has two parts that screw together. You cut the tip of your pastry bag to the bottom of the screw threads on the coupler and put the pointed part in the end of the pastry bag. The outer ring part screws on a standard size tip by enclosing it at the end of the bag. This way you can write the birthday name on the cake with a writing decorating tip and then unscrew the coupler and place a star tip on the bag to make star decorations.
This is considered a small or standard size coupler.