13/16" - at least that is the size for my honda 520S snow blower.
You need an 18 mm spark plug socket.
The spark plugs in a Honda VTX 1300 can be removed by first removing the spark plug wire. Twist the spark plug out, using a spark plug socket. Reverse the process to install the new spark plug.
Get a spark plug socket and unscrew the spark plug and replace with a new one.
most likely it will be a 5/8" spark plug socket.
By taking the spark plug wire off, and then using a spark plug socket with a ratchet and extension. It's not rocket science.
To change the spark plug on a Honda Rincon, first, ensure the engine is cool and disconnect the negative battery terminal. Remove the spark plug cap and use a spark plug socket to carefully unscrew the old spark plug. Before installing the new spark plug, check the gap and adjust it if necessary. Finally, screw in the new spark plug by hand, tighten it with the socket, reattach the spark plug cap, and reconnect the battery.
It is a 18 mm socket that works to get the spark plug out, it took me a while to figure it out.
19mm thin wall.
Remove the chrome cover, pull out the plug cable, use the spark plug socket with a ratchet.
18mm thin wall socket normal socket will not work
Take off the gas cap. Take off the big plastic cover with a socket and wrench.Then put the gas cap back on. Then pull of the spark plug boot. Then take off the spark plug with a spark plug socket and wrench. It should be 13/16" socket with 3/8" drive wrench. I Think the spark plug gap is 0.025 but you would have to look at a manual.