Pistons?

[Kwak81]

Sorry if this is the wrong place to post this. I recently bought a 2010 kx85 that my nephew is learning on. It started running poorly and bogging down so did some checks turns out to be the piston/rings. He ordered a standard piston and it arrived with a full gasket kit but when it removed the old piston it turns out it’s smaller than the original one ordered. The one I removed is 47.96 and the new one is 48.45. Is there any reason that a standard would be bigger than the original one in it? Or is the engine from a different year?

Thanks in advance folks.

[umberto]

I moved this over to the KX85 section so it won't get buried in the general questions. 

[Kwak81]

Thanks for that I’m new to the forum still finding my way round 👍🏻

[umberto]

You’re welcome. You’ll be an expert in no time.