TKR6731 - Shock Pistons(CNC, 2×1.7, flat/flat,13mm,2pcs). Part Number: TKR6731. With these optional pistons, it is now easier than ever to fine-tune suspension characteristics based on your needs. Made from precision machined self-lubricating delrin, these CNC pistons have two large 1.7mm holes and four small relief holes.