Autolite 303 Spark Plug

Autolite 303 Copper Resistor Spark Plug

Autolite 303 is a copper resistor spark plug built for OE-style replacement needs across classic Chevrolet and GMC applications. It is engineered for quick starts, steady acceleration, and improved fuel economy while maintaining the form, fit, and function expected in original-equipment service.

Compatible With Chevrolet Bel Air, Corvette, El Camino, Blazer, C10 Suburban, C20 Suburban, K10 Suburban, K20 Suburban, and GMC van and Jimmy applications listed below, the Autolite 303 supports dependable ignition performance in a wide range of vintage vehicles.

Key Features

• Copper center electrode core for consistent ignition performance
• Nickel center and ground electrode tip materials
• 5000 ohm resistor design for reduced electrical noise
• Standard/regular center electrode design with a single ground electrode
• Flat seat, 14.0 mm thread diameter, and 13/16 in. hex size
• Ceramic short insulator for OE-style spark plug construction
• Pre-gapped to 0.034 in. / 0.90 mm
• Removable nut terminal for common ignition wire setups

Product Details

The Autolite Copper Resistor Spark Plug line focuses on OE-style service parts for foreign and domestic vehicles. Part number 303 uses a copper core to support reliable spark delivery, while the resistor design helps control interference in the ignition system. Its flat seat, 0.374 in. reach, and standard 14 mm thread size make it a practical replacement choice for many classic Chevrolet and GMC engines, including 1950s and 1960s Bel Air and Corvette applications.

This part cross-references Champion Spark Plug 102 for the same application.

Common Issues This Part Can Help Address

• Hard starting caused by worn or fouled spark plugs
• Rough idle from inconsistent spark delivery
• Reduced throttle response during acceleration
• Ignition noise in resistor-equipped systems
• Maintenance replacement for aging OE-style plugs

Installation Notes and Tips

• Verify thread diameter, reach, seat type, and hex size before installation.
• Check the specified gap for your engine application; listed fitment notes include 0.035 in. and 0.025 in. requirements on certain vehicles.
• Use the removable nut terminal only with the ignition wire style specified for your vehicle.
• Inspect plug wires, distributor components, and coil condition during service to maintain ignition performance.
• Confirm the correct application for your Chevrolet or GMC engine before final tightening.

Quality Assurance

Autolite supplies ignition products for automotive aftermarket and original equipment use, with a focus on OE form, fit, and function. Part number 303 is built as an OE-style copper resistor spark plug for service on listed Chevrolet and GMC applications.

Fits 1950-1953 Chevrolet Bel Air, N/A. Fits 1953-1954 Chevrolet Corvette, N/A. Fits 1959-1960 Chevrolet Bel Air, N/A. Fits 1964-1970 Chevrolet El Camino, N/A. Fits 1967-1970 Chevrolet C10 Suburban, N/A. Fits 1967-1970 Chevrolet C20 Suburban, N/A. Fits 1969-1970 Chevrolet Blazer, N/A. Fits 1967-1970 Chevrolet K10 Suburban, N/A. Fits 1967-1970 Chevrolet K20 Suburban, N/A. Fits 1967 GMC G15/G1500 Van, N/A. Fits 1967 GMC G25/G2500 Van, N/A. Fits 1970 GMC G25/G2500 Van, N/A. Fits 1970 GMC G35/G3500 Van, N/A. Fits 1970 GMC Jimmy, N/A. Fits 1955-1962 Pontiac Laurentian, N/A. Fits 1959-1962 Pontiac Parisienne, N/A.