Which piston size to get?

[ratmac]

My 2018 ec 250 has 101 hours on the stock piston and i Will be doing a topend.

This bike has never been torn apart. Is there a way to know which piston letter to get?

 

[Wbdisco]

Should have a stamp on the cylinder of which size is in it. A,B, or C.

 

[wade_wade]

Inspect and measure the bore prior to purchasing a piston.

 

[ratmac]

Finally removed the head off my bike. After removing the carbon deposits an A and a 66.34 were visible. The bike has 120 hours. Should i get a 66.34 or a 66.35 piston?

The mechanics in my city don't have the proper tools to measure the bore with preci