Kibblewhite Precision Manganese Bronze Intake Valve Guide (+.002) 20-21022Precision machined guides Manganese bronze guide material is softer than nickel aluminum bronze valve guides Excellent heat conductivity which promotes long valve life Material hardness helps support valve guide longevity Guides can be easily reamed with a battery operated or electric drill and finished with a high quality ball hone Eliminates the need for expensive honing equipment that would be required for nickel bronze valve guides Machined to