The NGK D7EA is the correct spark plug for the Honda CB500K, CB550K, and CB550F inline-four engines. Sold individually — you need four plugs per bike.
The CB500K and CB550 use a different spark plug than the Honda twins. If you're buying an old CB500 or CB550, there's no telling what plugs are in there — and just because a plug threads in doesn't mean it's the right one. The D7EA is the Honda-specified copper-core plug for these engines. If you're doing carburetor tuning, keep a few sets on hand to read the plug tip color and gauge your fuel mixture.
Set the gap to 0.6–0.7 mm (0.024–0.028 in.) using a spark plug gap gauge before installation. Apply a small amount of oil to the threads and hand-tighten until snug.
Terminal nut vs. terminal stud: Each D7EA ships with a terminal nut installed. Unscrew it to expose the terminal stud threads — your spark plug boots connect to the stud, not the nut. It can be extremely tight. See our terminal nut vs. stud guide for details.
Copper-core plugs are ideal for carburetor tuning — keep extras on hand so you can read the mixture on a fresh plug. Light tan to chocolate brown means a healthy fuel mixture.
Unscrew the terminal nut on top of the plug to expose the terminal stud. The boots connect to the stud. Use pliers — it can be very tight.
The D7EA fits Honda inline fours (CB500K, CB550). The BR8ES fits Honda twins (CB350, CB360, CB450, CB500T). They are not interchangeable.
Four — one per cylinder. The CB500K and CB550 are inline-four engines.
Last updated: March 2026
