Valve locks, also known as valve keepers, are small, semi-circular components that secure the valve spring retainer to the valve stem. They are critical for maintaining proper valve spring tension and preventing the valve assembly from malfunctioning. Valve locks are typically constructed from high-strength steel and are available in various sizes to fit different valve stem diameters. When choosing valve locks, it's important to consider the specific application and the recommended locks for your vehicle's valvetrain system.