This listing is for a NEW Wiseco brand piston kit for a Yamaha AT2 125cc reed induction. This is 1.00mm oversize (57mm) piston kit and this kit consists of piston, rings and clips. The part number for this piston is 187P4.
Looked the piston up in my old parts book and found the following information
Yamaha 125cc AT-2 (reed induction)