Honda FourTrax Rincon TRX680FA5 2018 Owner's Manual page 150

Spark Plugs
10. Inspect the electrodes and centre porcelain for deposits,
corrosion, or carbon fouling. If the corrosion or deposits are
heavy, replace the plug. Clean a carbon or wet-fouled plug with
a plug cleaner, if available, or a wire brush. Inspect the spark plug
electrodes for wear. The centre electrode (12) should have a flat
tip and sharp edges, and the side electrode (13) should not be
eroded. If the electrodes and insulator tip appear unusually
fouled or burned, we suggest that you contact your Honda
dealer.
11. Discard the spark plug if there is apparent wear or if the insulator
is cracked or chipped.
12. Using a wire-type feeler gauge, check the spark plug gap (14). If
adjustment is necessary, bend the side electrode carefully.
The gap should be:
0.80 to 0.90 mm (0.031 to 0.035 in)
(13)
(12) centre electrode
(13) side electrode
140 Servicing Your Honda
(12)
(14)
0.80 to 0.90 mm
(0.031 to 0.035 in)
(14) spark plug gap