The method of achieving internal lubrication of the chains is known as sintering and consists of the high quality oil impregnation of the components during their manufacture. The steel bushings are forged with lubricant within the material structure of the steel. During this operation, the lubricant forms a micro thin layer between the pin and internal roller surfaces. Self-lubricating chains provide excellent service life without relubrication. In addition, self-lubricating chain pins are nickel-plated to provide a very smooth running surface that will not cause the self-lubricating bushings to wear. The link plates are black phosphate coated. Self-lubricating chains are interchangeable with standard roller chains. The use of self-lubricating chains can substantially reduce elongation in many applications. This provides an increased service life of the chain. The SKF Xtra Performance SLR Chains can also be used as a base for attachment chains, which are commonly required in the printing and packaging industry.