Large capacity E-Z Nurser prevents "gulping" and helps calves gain weight faster right from the start. The bottle, fashioned of a special plastic with pint markings, won't crack or break and lasts indefinitely. It's light and easy to clean and sterilize. E-Z Calf Nipple is rubber with cross-cut opening for full flow and air hole which prevents vacuum. Mouth of bottle measures 2-5/8" OD.