Molded nylon is used in hair combs and mechanical parts such as machine screws, gears, gaskets, and other low- to medium-stress components previously cast in metal.[87][88] Engineering-grade nylon is processed by extrusion, casting, and injection molding. Type 6,6 Nylon 101 is the most common commercial grade of nylon, and Nylon 6 is the most common commercial grade of molded nylon.[89][90] For use in tools such as spudgers, nylon is available in glass-filled variants which increase structural and impact strength and rigidity, and molybdenum disulfide-filled variants which increase lubricity. Nylon can be used as the matrix material in composite materials, with reinforcing fibers like glass or carbon fiber; such a composite has a higher density than pure nylon.[91] Such thermoplastic composites (25% to 30% glass fiber) are frequently used in car components next to the engine, such as intake manifolds, where the good heat resistance of such materials makes them feasible competitors to metals.[92]