Hey guys

Just got my first plane. It's a tower trainer 40 RTF which come with a Tower Hobbies .46 engine.
What plug should i use when i need to replace the plug that come with it?

I have a lot of o.S. #8 plug which i use for my cars. O.S. also recommends this plug for plane engines. When i compare the stock plug to a #8 plug i noticed the #8 plug was much shorter. If i dont use the washer that comes with the #8 plug then the lenght is the same as the factory plug.
I guess my question is can i use the #8 plug without the washer? or should i use another plug?

Thanks