GN 421 Nylon Plastic Hollow Knurled Knobs with Threaded Stud feature RoHS-compliant knobs made of black nylon plastic that have smooth, glossy finish and max heat resistance rating of 230°F. Other colors are available upon request, and, straight knurling on knob surface promotes secure grip for fine adjustments or clamping. Threaded stud is zinc-plated steel (molded-in), and various threads and stud lengths are available.