MSD designed this 86213 Crank Trigger Wheel as a replacement wheel for Big Block Chevy engines. Four magnets secured in this aluminum trigger wheel pass by a stationary non-magnetic pick-up to trigger the ignition. This "flying magnet" design produces accurate trigger signals so a non-magnetic pick-up cannot be falsely triggered. Mounting instructions included. Note: Non-magnetic pick up sold separately. MSD 86213 Crank Trigger Wheel Features: Fits Big Block Chevy engines Color: Black Bracket Material: Billet Aluminum Wheel Width: 3/8” Diameter: 8 in. Hardware Included: No Quantity: Sold individually Street cruisers as well as Top Fuel dragsters trust MSD's ignition systems as the industry leader for over 40 years. MSD continues to push the envelope with cutting-edge ignition technology as well as intake manifolds and EFI systems.