This is a genuine Dremel replacement part, it is sold individually. The purpose of the Collet Nut is to secure the collet with the bit of your choice in the shafts assembly of the Dremel tools shown below. By pressing on the lock assembly on the tool and using the wrench provided with your tool you can secure or release the Collet Nut.
This is a Genuine Manufacturer Approved replacement part used on some Dremel Rotary Multi-Tools. This part provides the firm grip for holding a bit in a tool. This Collet is for using bits with 1/8" arbors. Due to prolonged, heavy use a collet may need to be replaced. Collet Nut is sold separately.