NGK 6431 BU8H Surface Gap Spark Plug.

NGK's Surface Gap Plugs are Nearly Immune to Pre-Ignition, and Usually Require a Special High Energy Ignition System. They Can be Susceptible to Fouling, Especially in Colder Applications, but May be Necessary in High Compression Applications.

Fits Mariner and Mercury outboard engines.

Specifications:
Shell

Thread Size: 14mm

Thread Pitch: 1.25mm

Seat Type: Gasket

Resistor: No

Reach: 12.7mm (1/2")

Hex Size: 13/16" (21mm)

Terminal Type: Solid

Overall Height: ISO

Gap: .016" (0.4mm)

Center Electrode

Material: Nickel

Type: Standard

Size: 2.5mm

Projection: Non-Projected

Ground Electrode

Material: Nickel

Type: Surface Discharge

Torque Specs: Cast Iron: 18-25.3 lb. ft. Aluminum: 18-21.6 lb. ft.

Brand: NGK

Heat Range: 8