Class 14 material is a designation of the Resistance Welding Manufacturers Alliance (RWMA). It describes a pure Molybdenum material with good conductivity and excellent strength at high temperatures and forces. It is used as electrodes for cross were welding and electrobrazing.
Class 14 is a very heat tolerant refractory material second only to tungsten. It can be machined with conventional carbide tools. It is used in similar applications to tungsten, where there is a lot of heat and force. It is nearly as strong as tungsten but is definitely more ductile. Cross Wire welding and electrobrazing highly conductive materials is a frequent application for Moly.
The product description and properties of Class 14 can be found in the Resistance Welding Manual section 18-3, available at RWMA/AWS.
There are other Class materials with other properties all shown in the above reference. Their properties allow for the welding of work pieces with properties and applications different from those Class 14 is used for.