Spark plug conundrum

[Changy]

Hi all,

I have two Stihl RM545.0T mowers (Briggs and Stratton EVC300) in for service. One has a Champion XC92YC spark plug, but the other has an NGK BPR5ES.

Both of the mowers start first or second pull and run well. I checked the Briggs & Stratton site, and they list the Champion plug.

My question is, what is the difference between these two plugs? Physically the NGK protrudes more, but the boot fits securely.

I'm not sure what to make of it. 

[Mick]

I'm not sure on the difference without researching, but we only use NGK plugs, and would fit a BKR5E which is the same profile as the Champion requiring the smaller socket to remove and refit it.