Class 2 material is a designation of the Resistance Welding Manufacturers Alliance (RWMA). This is a group of copper alloys with high strength and electrical conductivity. Class 2 is the most used material in the resistance welding industry. As electrodes it is used for welding bare and coated steels.
Class 2 Bar Stock
The product description and full properties of Class 2 can be found in the Resistance Welding Manual section 18-3, available at RWMA/AWS.
AWS Standard J1.3 Specification for Materials Used in Resistance Welding Electrodes and Tooling
Class 2 has very good strength and conductivity along with good heat resistance. Thes values have made it the most used material in the industry. It is fabricated into electrodes, holders, shanks, threaded adapters machine components and many other products in the resistance welding industry.
There are other Class materials with other properties shown in the above references. Their properties allow for welding work pieces with both higher and lower resistances and strengths than steel.
Reference: RWMA - Resistance Welding Manual 4th Edition
AWS J1.3 - Specification for Materials Used in Resistance Welding Electrodes and Tooling