Nodular Iron Performance Diff Cover. Engineered for Off-Road. For full-performance differential covers that are engineered with the serious off-roader in mind, get the same name you trust for all your drivetrain products-genuine Spicer. Manufactured from high-strength nodular iron, Spicer performance diff covers are built to meet the demands of any environment. Don't trust a knock-off to protect your intricate differential parts. Count on the legendary Spicer brand.