Briggs and Stratton spark plug chart: a complete guide. If you are searching for the right spark plug for a Briggs engine on a pressure washer, generator, or utility machine, this is the place to start. Flathead engines take an RJ19LM plug. OHV engines take an RC12YC plug. Both gap at 0.030 inches. The chart covers part numbers, NGK, Champion, and Autolite cross-references, torque specs, and the Quantum date code rule that catches most people off guard. The thread reach mistake is also covered. A long OHV plug will screw into a flathead engine, but the projected tip can hit the piston. Short plugs in OHV heads cause carbon buildup and misfires. Match the plug to the engine family first.