18MM
The correct spark plug for this motorcycle is: NGK D8EA
Spark plugs use SAE and not Metric. The one that fits it is the one that fits it.
what is the spark plug gap for a 1979 Honda odyssey
5/8"
Get a spark plug socket and wrench that fits the plug body and remove it by turning counter-clockwise.
18 mm
11/16" (18mm) deep well socket
The BPR6ES spark plug typically requires a 5/8-inch (16mm) socket for installation and removal. This size is standard for many automotive spark plugs. Ensure you have a spark plug socket with a rubber insert or magnet to help secure the plug during installation.
The CR9EH-9 spark plug needs a 16mm or 5/8" socket.
NGK D8EA/DR8EA/DR8EIX or equivalents.
For XR and XL 250 (pre 83 year), use NGK D8EA
most 50cc 4 stroke takes 5/8