1/4″ Mild Steel Weld-on Base Only

Precision Exhaust Gas Temperature Sensor Mounting Solution

The 1/4" Mild Steel Weld-on Base Only is the foundational component for installing professional-grade Exhaust Gas Temperature (EGT) monitoring systems. In the world of high-performance engine tuning, accurate thermal data is the difference between a reliable tune and catastrophic engine failure. This weld-on boss (bung) is engineered specifically to provide a secure, leak-free mounting point for thermocouple compression fittings on mild steel exhaust manifolds, headers, and dump pipes.

Engineering for Thermal Accuracy and Structural Integrity

Fabricated from high-quality mild steel, this base is designed to match the thermal expansion coefficients of standard mild steel exhaust components (such as steam pipe manifolds or standard headers). This material compatibility is critical; it prevents the weld cracking and separation that frequently occurs when mixing dissimilar metals under the extreme thermal cycling of an exhaust system (often exceeding 900°C / 1650°F). The boss is precision-machined to accept standard compression fittings used with 1/4-inch (6.35mm) probe diameter thermocouples.

Unlike generic plumbing fittings, this base features a contoured profile and sufficient wall thickness to support the sensor probe against the high-velocity exhaust pulse. When welded correctly, it becomes an integral part of the exhaust structure, ensuring the probe tip remains fixed in the center of the gas stream for the fastest and most accurate response times. This is essential for detecting individual cylinder trim issues or dangerous lean conditions before they cause piston damage.

Operational Benefits for Fabricators and Tuners

• Optimal Weld Penetration: The uncoated mild steel surface is ready for TIG or MIG welding, ensuring a porous-free, structural bond with the manifold.
• Universal EGT Compatibility: Designed to accommodate the compression fittings found in most high-end aftermarket EGT kits (including Haltech, MoTeC, and RaceGrade) that utilize 1/4" probes.
• Leak-Proof Sealing: Provides a rigid, non-deforming thread interface for the compression fitting, ensuring the olive seals correctly and preventing exhaust leaks that could skew wideband O2 readings.
• Cost-Effective Fabrication: Allows for the creation of custom multi-cylinder EGT setups on fabricated manifolds without the expense of stainless steel bungs if the header material is mild steel.

Technical Specifications

Installation Notes

This product is the Base Only. It does not include the compression fitting nut, ferrule, or the thermocouple probe itself. It is intended for custom fabrication projects where the installer is welding bungs onto an exhaust system to accept an existing sensor kit. Professional welding is required. Ensure the bung is positioned to allow the probe tip to sit in the center of the exhaust flow without touching the manifold walls.