Ordered this kit for 2013 KTM 85 sx. Description says "standard bore'" but apparently, KTM produces engines with "A", "B", and "C" bores from the factory. These are just three different size pistons that vary by a fraction of a millimeter and are fit to each motor individually to help account for variance in machining and plating of the bores. The piston I received was a "B" unit and it turns out that our bike was fitted with a "C" piston from the factory. I wish that the item description had spelled this out so that I could have gotten the "c" piston instead, but there was no mention of this in Motosport's description. I installed the "b" unit and I'm sure it will be fine since I will replace it in about 20 hours anyway.