This is a 1/4 inches-28 taper thread (SAE-LT), straight, 0.52 inches grease fitting. It is used on most auto vehicles and on industrial equipment. SAE-LT threads conforms to society of automotive engineers lubrication thread specification. The ball check prevents dust and dirt contamination. These fittings have a ball check in the head to prevent dirt and grit from getting into the fitting, heavier wall thickness for extra strength, are zinc plated with a yellow passivated finish for maximum protection against corrosion, and have a stress relieved and tempered carbon steel spring. Every fitting is individually inspected and batch tested to 5,000 PSI and are designed to meet the demanding requirements of most automotive, agricultural, industrial, marine, truck, federal and construction equipment needs.