These threadlockers work with metal fasteners to prevent loosening due to vibration. They fill the space between the threads of bolts and screws to hold them in place and form a barrier around the threads to prevent leaks, corrosion, and rust. Threadlockers are color-coded to represent their locking strength and other unique properties. They are anaerobic, which means they begin to cure in the absence of air, and in the presence of metal ions when threads are engaged. Threadlockers can be applied directly to fasteners with active metal ions such as plain steel, copper, iron, and brass. For inactive metals such as stainless steel, aluminum, and coated or plated metals, threadlockers require a primer to prepare the surface and accelerate curing. Primerless threadlockers work on both active and inactive metals without the need for a primer.