GMT the World's Most Comprehensive Range of Carbide Threading Inserts. None of the large cemented carbide manufacturers have anywhere near the same range as that available from GMT. The reason is simple. Threading is a fairly small part of all machining operations, and has been neglected by major carbide companies who offer only a limited range of the most common profiles. On the other hand GMT has a range that covers all of the threads used throughout the world. The main product range is concentrated on inserts and toolholders for threading. In simpe terms, GMT is a specialist.