The Eagle Plastic Devices Collet Knob System includes collet knobs in 15mm and 21mm sizes for 6mm and 6.4mm shafts. The 15mm collet knob is available with a marker line. The collet knobs are secured to the shafts by a proven collet tightening method. With its modular design, multiple accessories can plug into the knobs for a customized look. Eagle Plastic Devices also offers color coded caps in 15mm and 21mm sizes either plain, with a marker line, or a dot. Pointers and Nut Covers are available in multiple colors in a 15mm size (pointers also available in 21mm).