JW Pet Company Feeder Cup features: - Unique washer system makes it a breeze to fit all size and style cages - Easy to clean & dishwasher safe too! - Screws into the horizontal and vertical bar cages to guaranty a secure fit - Clear plastic shield keeps food and debris from falling outside the cage The shield and the cup placement a few inches into the cage to prevent the bird from shoveling out his seed onto the floor. Because it is clear, birds don't mind sticking their heads into it (unlike opaque shields) Small: 3” with 2” diameter. Medium: 5.5” with 3” diameter Large: 7.5” with 3.5” diameter