Plain Piping Tip Ateco 805
you can create smooth-edged patterns ideal for creating a single dollop of frosting or wide swirl designs. This tip is also great for filling macarons and cannolis without making a mess. Plus, its medium size is perfect for icing confectionary creations quickly and efficiently. It is also compatible with the Ateco 402 coupler and Ateco 407 coupler using the 1" coupler ring, making it easy to switch tips without changing the pastry bag.
 
Overall Dimensions:
Opening: 1.85"
Bottom Diameter: 2 1/4"