12101520 - Tweco 21-62-FAS Flat Arc Spot MIG Nozzle, 5/8" Bore (2-Pack)

Technical Overview of the Tweco 21-62-FAS Nozzle

The Tweco 21-62-FAS (Stock No. 1210-1520) is a specialized MIG welding nozzle engineered specifically for arc spot welding applications. Part of the industry-standard 21 Series, this nozzle is compatible with Tweco No. 1 (180 Amp) and No. 2 (250 Amp) air-cooled MIG guns, as well as other MIG guns that utilize the 21 Series consumable platform. The 'FAS' designation stands for Flat Arc Spot, indicating the nozzle's unique geometry designed to facilitate direct contact with the workpiece.

Technically, the nozzle features a 5/8-inch (15.9 mm) bore orifice, which provides a balanced shielding gas envelope suitable for the short-duration, high-current bursts typical of spot welding. The nozzle body is machined from a high-conductivity copper alloy, selected for its superior thermal dissipation properties and resistance to spatter adhesion. The unit utilizes a 3-piece construction consisting of the outer copper shell, a high-temperature electrical insulator, and an internal insert. This design ensures electrical isolation of the nozzle from the contact tip and gas diffuser, preventing accidental arcing when the nozzle face is placed flush against the metal surface.

The adjustable slip-on connection mechanism allows the operator to fine-tune the nozzle position relative to the contact tip, although for spot welding, the contact tip is typically recessed significantly to accommodate the arc length required within the nozzle cup. The flat face of the nozzle acts as a mechanical stop, guaranteeing a consistent standoff distance (CTWD) for every spot weld, which is critical for maintaining consistent weld nugget size and penetration depth in production environments.