Here, you are looking at the HKS 2.1L FA20 Stroker Kit Replacement Piston Kit 2013-2021 BRZ/ FRS/86. 

This kit is only to be used as a replacement for the pistons found in the 21004-AT003 / 21004-AT004 stroker kits and is not suitable for use with rods/crank outside of the HKS 2.1L Capacity upgrade.

Piston Kit:

• Carefully selected specially forged raw materials used to improve durability

• Recessed pistons account for high-lift HKS camshafts
  

• In order to meet high power requirements, the compression ratio was optimized through strength analysis and testing, allowing for flexibility in the setup, and the use of high boost levels. 

• The piston crown had 3D design in consideration of the stock direct injection system and tumble flow

• Depending on the head gasket used, varying compression ratios are achievable
  

• Molybdenum-coated pistons reduce friction

Stock Bore Compatibility: 

• To maintain block strength, this kit retains the factory 86mm piston bore

• No need for boring, honing, or sleeves makes this a cost-effective install