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. Lumax is a manufacturer of lubrication and fluid management products. Our products, including grease guns, manual and electric pumps, funnels, drains, grease fittings, filter wrenches, and accessories, are built to the highest standards and incorporate many proprietary features. Lumax's mission is to provide professionals and consumers with innovative and high-quality products to get the job done right. Product development at Lumax goes beyond the physical product, to a deeper understanding of the end-users' needs. Engineered with the "user-in-mind, " Lumax products are built to the highest standards and incorporate many unique features that make work easier, faster and cost-effective. We have a passion for the design process. We listen to our customers and their ever-expanding requirements. Our unique products lead the field in design, quality, and performance.