yz125 piston size question

I have a 2000 yz125 that i an going to do a top end on. The cylinder is maked B. If i use a Wisco piston do they make more than one size? If i go with an OEM Yamaha piston should i use a B piston? or i have also read that you should run a D size piston in all cylinders A,B,C,or D if the cylinder is not new. Some more insight on this would be helpful.

Both my 125 and 250 cylinders are marked but that never made a differance as to which piston I put in. Just get the right one for the year of the bike along with the right bore (std or overbore).

The difference in size between the letters is hardly measurable, that's why Wiseco only makes one size. You are correct, you should run a "D" piston if using OEM.

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