This is the new yellow zinc 9" booster as used on 79-81 WS6 4 wheel disc brake Trans Am and Formula. Following in the footsteps of our very successful black 9" booster ( 0CB-100) This booster has not been available for many years, PTFB has recreated a version to satisfy both the restorers as well as the hot rodders and customizers. The yellow zinc gives it that factory look. Features and benefits over standard 11" brake boosters. - 30% more brake assist. - Helps improve braking with bigger cams and low vacuum. - Added clearance for tall valve covers. - Universal adjustable pedal push rod. - More flexible fitment for a wider range of applications. - Fits 79-80 as well as 81 master cylinders.