Sleeves identified by code EN170H13 are precision-machined components used in the MAN L21/31 engine to provide alignment, wear protection, and dimensional stability between mating parts. Typically installed in high-load or high-friction zones, these sleeves act as protective interfaces that safeguard major engine components from direct wear. Made from high-quality alloy steel, they offer excellent resistance to abrasion, thermal stress, and mechanical loads, thereby extending service life and reducing maintenance requirements in demanding operating conditions.