Manganese-bronze alloy valve guides, used to prevent damage to expensive valves; high heat transfer and durability. Must be honed to size after installation. Guide-to-valve clearance of .002" intake and .0025" exhaust must be checked after installation in the event of crush. These have the groove machined at the top to accept ADU4905 seal. Sold per set of eight (8). Ref: SEN0001, C-AJJ4037.