The Aviator Harness Leash are made from high quality nylon and rubber shock cords that expand as much as 100% depending upon the health and strength of your parrots or birds.X-Small Aviator Harness for birds weighing 110-190 grams:Quakers,Senegal,Doves,Pigeons,Med. Parakeets,Indian Ringneck,Port Lincoln,Rainbow Lories,Rosellas,Noble/Hahns Macaw, Lg.Conures (Suns,Jendays, Nanday,Blue Crown Conure),White Belly & Black Headed Caiques,Plum Head.