11/16" (18mm) deep well socket
NGK Plug DPR8EA9
18MM
Spark plugs use SAE and not Metric. The one that fits it is the one that fits it.
5/8"
Get a spark plug socket and wrench that fits the plug body and remove it by turning counter-clockwise.
18 mm
The CR9EH-9 spark plug needs a 16mm or 5/8" 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.
dpr8ea9 is a resistor plug dp8ean is non resistor.
18 mm spark plug socket
most 50cc 4 stroke takes 5/8
You will need either a spark plug wrench or socket that fits the plug. The socket will need to be not only the right size, it will need to be deep enough to allow the socket to engage the nut built into the plug. Be careful not to force the plug if it is seized as breaking it off leads to major projects. Most plugs unscrew easily.