What spark plug?

[Kosmo]

The original spark plug indicated for my WH lawn tractor with the Kohler KT17QS engine is the Champion RV15YC. All the plugs I'm seeing are either RV15YC4 or RV15YC6. From my understanding the last number only has to do with the gap of the plug and therefore I could use either of these plugs and just regap them to specs? Am I correct? Thanks

 

[Fixemall]

Use the 15yc4 or go to NGK( ur4 I think?) gap accordingly and you will be fine.