Chevrolet Small and Big Block - Straight Mount Holes;3.73:1 Gear Reduction; Additional 25% cranking speed; Also Available in Red; Billet aluminum adjustable mounting block; For use on blown alcohol engines, magneto ignitions, or any engine requiring higher cranking RPM; Heavy Duty high temp solenoid for 12-16 volt systems; Plated disc and contacts reduce arcing and increase continuity; Used for 153 or 168 Tooth Flywheels;