415 Sprint Racing Chain Series Features RK’s proprietary Ultra Thin U Seal Rings. U-Rings have a seal thickness less than 50% of the common O-ring seal, making it possible to design a Sealed Chain with the weight of a Non-Sealed Chain. Running a Sealed Chain on race machines can minimize the elongation of the chain, keeping high horsepower transmission efficiency throughout the duration of the race. HRU Racing Chain Series are designed strictly for RACING ONLY, NOT FOR STREET USE.