These forged 3-7/8" bore stroker pistons for 1999-'16 HD® big twin are required for the S&S 106" stock bore stroker kit with 4-1/2" stroke flywheels. They are compatible with stock or S&S® Super Stock® cylinder heads. Stock 88" cylinders may be bored to fit these pistons, or S&S has replacement cylinders available.. +.010" oversize.