Often used on earth movers, mining equipment, and other heavy machinery, these fittings have a T-shaped top that holds the dispensing tip in place so it won’t pop off when adding grease. They're best for machinery requiring high volumes of grease because they let more grease pass through than standard grease fittings, thanks to a larger opening. An integral check valve prevents grease from leaking when pressure causes backward flow. The valve stays closed when not in use to keep out dirt and other contaminants.