Header Bolt Kit - 12pt. GM LS

The ARP Header Bolt Kit – 12pt. GM LS is a premium fastening solution engineered for GM LS-series engine builds where reliability under extreme load is non-negotiable. This complete set of 12 chromoly header bolts addresses a critical weak point in high-horsepower and forced-induction applications: fastener failure due to thermal cycling and vibration. Each bolt features a 12-point head design that ensures superior grip and torque accuracy without rounding, a specification favored by engine builders who demand precision and repeatability.

Each fastener in this kit measures 8mm diameter with 1.25mm thread pitch and extends 0.984 inches in length—dimensions matched precisely to GM LS header flanges. The chromoly construction provides superior tensile strength compared to standard steel, critical for absorbing combustion pressure spikes and vibration cycles in turbocharged or supercharged builds. Black oxide coating delivers corrosion resistance while maintaining thread integrity, and the included washers distribute clamping load evenly across the header flange surface, preventing stress concentration that leads to thermal cracking. This combination of materials and geometry keeps fasteners tight through dyno sessions and extended track duty.

Buyers building LS engines for street performance, track use, or competitive applications depend on header bolts that won't shear or loosen under sustained load. OEM fasteners are frequently replaced in these builds because they lack the material specification needed for modified power levels. ARP fasteners are purpose-built for this application, offering the marginal reliability gain that separates a leak-free system from a catastrophic header separation event. The 12-point head geometry also simplifies torque specification—fewer rounded corners mean builders can torque to specification with confidence, reducing the risk of under-tension or over-tension failures.