All Isoloc joints are cut with straight bits and we offer two variants; a two flute spiral upcut in High Speed Steel and a Solid Carbide version. The spiral upcut design cuts cleaner, faster, leaves a smoother finish and dramatically reduces tearout. Although both produce excellent results, the solid carbide versions are stiffer and they hold a keen edge longer than the HSS. The performance of less expensive HSS bits is comparable to Solid Carbide but they loose their edge more quickly. Choose the bit that best suits your needs and budget.