Champion RTM77N

Thread size: M18
Thread reach: 1/2"
Hexa size: 7/8"
Ground electrode: Ni (4x)
Cetre electrode: Ni
Finish: Unshielded
Heat ragen: Cold
The following engine manufacturer are widely use this spark plugs :

Waukesha, Case, Climax, Cooper - Bessemer, Dorman, Fairbanks Morse, John Deer, MEP Industries, Minneapolis-Moline, Rathbun Jones, Roiline, Superior