Billet Filler Cap 3in -12 Thread

The Billet Filler Cap 3in -12 Thread by Peterson Fluid is a precision-engineered aluminum filler cap designed for cooling system and reservoir applications in automotive and powersports builds. This component seals fluid entry points while providing reliable access for maintenance and top-offs. Built to OEM specifications, it serves as a direct replacement or upgrade for stock cooling system caps, making it essential for builders who demand durability and professional-grade materials in their engine bay.

Machined from solid billet aluminum and finished in vibrant red anodizing, this filler cap combines strength with corrosion resistance. The 3-inch outer diameter and 12-thread configuration ensure a secure, rattle-free fit on compatible reservoir threads, while the anodized coating protects against oxidation and extends service life in harsh underhood environments. The compact footprint (4.6 x 1 x 5.1 inches) allows seamless integration into tight engine compartment layouts without sacrificing ergonomic access during routine maintenance.

This billet filler cap is ideal for custom cooling systems, race engines, hot rods, and high-performance street builds where OEM aesthetics clash with builder vision. It pairs well with Peterson Fluid's complete line of billet aluminum cooling components and works across domestic and import platforms using -12 thread reservoirs. Installers simply thread the cap onto compatible filler necks—no special tools required—and benefit from the professional appearance and reliability that distinguishes hand-built engines from stock setups.