Presented wrenches are used mainly to tighten or unscrew the nut of an ER collet chuck, though they can also be used for other purposes.




First one is the hook wrench with one tooth, claw or nose. The element that hooks the nut groove has many names. This wrench is compatible with standard ER type T2 nuts. It matches a certain diameter range, for example ER40 wrench is used with nuts of 55 to 63 mm diameter.


Wrench sizeNut diameter [mm]
ER25 38 - 42
ER32 45 - 52
ER40 55 - 63
ER50 78 - 85


Due to a fact that this wrench has got only one tooth and it's designed for a range of diameters, it can be used not only with ER nuts, but also with other nuts with grooves, for example bearing nuts. A wrench with one claw allows for approach from the front or from the side of a nut.




The next wrench i a multi-point hook wrench, which is likewise used to tighten type T2 nuts. Four hooking points guarantee steady and stable position of the teeth in the nut. This wrench matches only one specific ER nut size, e.g. ER25, ER32, ER40 and so on.




ER MINI wrench is a variant of a multi-point wrench. As the name suggests it's used only with MINI type nuts. These wrenches are produced in sizes from ER8 to ER25. There are more hooking points on the perimeter of this wrench than in the previous (four-point) wrench. They also differ in the design of the teeth. In this case they are longer and pointed.

It's worth mentioning that ER MINI nuts have a different inner thread size than their standard counterparts, for example ER16 MINI has a M19x1 thread, whereas type T1 ER16 (hexagonal) has a M22x1,5 thread. ER MINI nuts are mainly used in collet chucks for tools with a cylindrical shank.




Open-end wrench can be used to tighten T1 type nuts. The only reqirement is to apply the right size for the hexagon of the nut.




Sometimes the manufacturers of collet chucks publish torque values for the ER nuts. A torque wrench with an appropriate hook matching the ER nut model should be used then.

The table below shows the torque values ​​for a specific nut size.


Collet sizeThreadMax tightening torque
ER8 M10x0,75 8 Nm
ER11 M10x0,75 25 Nm
ER16 M22x1,5 50 Nm
ER20 M25x1,5 75 Nm
ER25 M32x1,5 85 Nm
ER32 M40x1,5 105 Nm
ER40 M50x1,5 150 Nm




Sets of hook wrenches also exist. They are very economic, because a set of few adjustable wrenches covers a wide range of nut sizes. Single wrench matches several nut sizes, therefore it's possible to use it in a variety of tasks. In addition to that: laser-cut designations showing the range of matching nut sizes help pick the right wrench. Some of them have an interchangeable hook with a round pin. It can be used with drill chucks or vise handles.


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