Built in self-Release design and tools never get stuck in holder. Use with any standard ER collet chucks for coolant-thru tool applications. Each collet is well packed in separate protective container with label. Hardened and precision ground. Performance stability, high accuracy. in use. Widely used, boring, milling, drilling, silk attack, sculpture, CNC, and other processing. Colour: black + silver Material: 40CR Size: Spring Collet: 1mm, 2mm, 3mm, 4mm, 5mm, 6mm, 7mm, 8mm, 9mm, 10mm, Extension Rod: C20-ER16A-32L-10MM Package Contents: 10 * ER16 Spring Collet 1 * Extension Rod Only the above package content, other products are not included. Note: Light and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is +/- 1-3cm.