ER Collet Chucks

The Collet Chuck

A chuck plays a pivotal role in maintaining the stability of an electrode, and choosing the right chuck for your application deserves careful deliberation. For many applications—especially on a tight budget—standard jawed chucks are adequate. For those applications requiring the greatest possible precision, these kinds of compromises can be unacceptable. It is for these types of applications that the collet chuck was developed.

A collet, sometimes referred to as a collet chuck, is a type of collet with a tapered exterior that generates clamping force when pulled into a matching sleeve. This novel clamping mechanism generates a clamping force superior to that generated by the scroll gear of a standard self-centering chuck, and means that a collet chuck holds its tool more reliably and resists loosening more than a standard drill chuck. Additionally, a collet chuck tightens equally across its entire circumference. The additional points of contact and even distribution of clamping force gives collet chucks a more accurate hold. In spite of these advantages, collet chucks are not for everyone.

Developed as a specialized solution to serve a more demanding niche of the machining market, collet chucks are not as well suited to general purpose use as their more common counterparts. Since the entire collet is flexed when inserted into its sleeve, there is a practical limit to the diameter range of compatible electrodes, which is typically 1 mm for ER collets. For EDM machines drilling into a diverse set of parts requiring a wide range of electrode diameters, collets are inefficient. This and the additional cost of collets should be taken into consideration when choosing a chuck.

ER Chucks

The ER chuck was initially developed by Swiss company Rego-Fix and has since become one of the most prevalent collet chuck types in the world. We offer ER chuck sizes from ER8 (.5 mm/.19”) to ER40 (3 mm/.118”), covering all tool diameters in between. Standard and coolant-thru ER chucks are available.

ER Size




13mm (.51″)

8.5mm (.33″)


18mm (.708″)

11.5mm (.45″)


27.5mm (1.08″)

17mm (.67″)


31.5mm (1.24″)

21mm (.83″)


34mm (1.34″)

26mm (1.02″)


40mm (1.57″)

33mm (1.3″)


46mm (1.81″)

41mm (1.61″)


60mm (2.36″)

52mm (2.05″)