These are familiar in most aviaries and have a multitude of uses.
A hayrack to hang dried greens or salad leaves.
Also work great to hold nesting material both inside of right outside of the cage where the birds can easily grab some nesting material.
Nest building is a healthy exercise for your cage birds and this keeps the nesting material clean and off the floor:)
Plastic and comes in Green, Yellow or White. Approximately 3"x3"