These collets are used to securely hold your end mills into your spindle during milling. ER-20:Length: 31.5 mmDiameter: 21 mmRange: 1—12 mmER20 Collet - 6mmSKU: 151Quantity*Add to CartRETURN & REFUND POLICYNon-Refundable SHIPPING INFO2-3 Days for Available stock Items 7-14 Days for Out of Stock Items