300M - Weldcraft 300M Medium Back Cap for 17/18/26 Series Torches (2-Pack)

Technical Overview of the Weldcraft 300M Medium Back Cap

The Weldcraft 300M Medium Back Cap is a critical component designed for use with the widely utilized 17, 18, and 26 series TIG welding torches. As a genuine Weldcraft product, now under the Miller Electric umbrella, this back cap is engineered to meet strict manufacturing tolerances, ensuring a reliable interface with the torch body. The primary function of the back cap is to apply axial pressure to the collet, which in turn secures the tungsten electrode within the collet body. This mechanism is vital for maintaining electrical conductivity and preventing electrode slippage during the welding process.

Constructed from high-performance, heat-resistant phenolic materials, the 300M is built to withstand the thermal cycling and reflected heat common in high-amperage TIG applications (ranging from 150A to 350A depending on the torch model). The medium form factor of the 300M offers a strategic advantage in specific welding scenarios. While long back caps allow for the use of full-length (7-inch) tungsten electrodes, they can be obstructive in tight spaces. Conversely, short back caps offer excellent access but require the tungsten to be cut down significantly. The medium back cap provides a compromise, allowing for the use of partially consumed tungsten electrodes while offering a lower profile than the standard long cap.

Crucially, each 300M back cap comes equipped with a high-quality O-ring. This seal is essential for the integrity of the shielding gas coverage. A compromised or ill-fitting back cap can introduce atmospheric air into the gas stream (venturi effect), leading to porosity and weld contamination. By using genuine Weldcraft parts, operators ensure a gas-tight seal at the rear of the torch. This package contains two (2) medium back caps, providing a necessary redundancy for industrial environments where downtime must be minimized. It is compatible with air-cooled WP-17 and WP-26 models, as well as water-cooled WP-18 models, and is generally interchangeable with equivalent torches from other manufacturers such as CK Worldwide and Radnor.