Guide, Product Focus

CNC Tool Holders in the Marble and Glass Industry

Cnc Tool Holders Blog

If you are a CNC machine operator, you will be familiar with the use of CNC tool holders that allow you to connect various tools to the electrospindle of the CNC machine.

The functions of a CNC tool holder:

  • Allows the tool to be plugged to the electrospindle
  • Allows the transmission of force and motion from the electrospindle to the tool
  • Makes sure that the tool rotates in a safe, precise and concentric way even at high rotation speeds
  • Allows an easy and fast removal of the tool both manually (quick release) and through automatic tool changing systems (a system that includes a tool magazine and tool forks)

The Standards of the CNC Tool Holders

The CNC tool holders follow rules and standards, which have been defined by the AMT: Association for Manufacturing Technology. AMT is an organization that among other activities includes the standardization of tool holders used in manual machines and CNC work centers.

The three main standards for the CNC tool holders used in marble, glass, wood and mechanical sectors are:

  • ISO DIN 69871 which identifies ISO tool holders (ISO 30, ISO 40 and ISO 50)
  • JIS (Mas 403) which identifies the BT tool holders (BT 30, BT 40, BT 50)
  • ISO DIN 69893 which identifies HSK tool holders (HSK-A, HSK-B, HSK-E, HSK-F)

The parts of a CNC Tool Holder

A CNC tool holder generally consists of:

  1. Pull Stud (only in ISO and BT)
  2. Conical body
  3. Flanges
  4. Tool fitting

You can see in the following drawing the ISO / BT tool holder and the HSK tool holder with these various parts.

Parti Cono Mandrino Cnc Amastone

The CNC tool holder’s Pull Stud

The pull stud (retention knob) is a fundamental part because it connects the electrospindle to the CNC tool holder cone in the ISO and BT families. The pull stud can be one of two types: “with corners” or “radius”.

In the case of a pull stud with angles in the electrospindle, there will be a system of a petal clamp that hooks the cone to the machine.

In the case of a radial pull stud, the hooking system is a ball bushing.
The pull stud is a real consumable item because it is subjected to strong mechanical stress and because of this, we recommend checking and replacing it regularly in case they are damaged or worn. A damaged pull stud (perhaps due to the inevitable corrosion over time) can also break and cause damage to the piece being worked.

Pull Stud Of A Tool Holder Amastone

The “Body” of a CNC Tool Holder

By body we mean the conical part of the CNC tool holder and it depends on the standard on which the tool holder is based. The ISO standard (DIN 69871) and BT (MAS 403) have a long and easily identifiable conical body while the HSK provides a much shorter conical part.

In ISO models the dragging occurs only by coupling in the cone, by friction, while in HSK, because the body is shorter, the dragging takes place by coupling both on the conical part and on the flange. When the CNC tool holder goes into the electrospindle, the petal collet pulls and couples both cone and flange. This coupling is more stable in HSK than in ISO. The body is a bit different between ISO and BT. In ISO the body cone is 68.4 mm high while in the BT it is 65.4 mm. Thanks to this difference of 3 mm the standard succeeds in obtaining a coupling both on the cone and on the flange.


By flange or groove, we mean the part that acts as a hook to the CNC tool holder. Again, there is a difference between the ISO cones and the BT cones. In the ISO CNC  tool holders the flanges have pass-through cuts while in BT the cuts are not pass-through. Among the exceptions, there are cones without cuts like those used by Brembana.

Tool Holders Flanges Amastone

Cuts in the flanges

A CNC tool holder can have two cuts in the flanges, and when it does, these cuts can be the same or different. Looking at a tool from the bottom, it is easy to see if there is a difference between the two cuts. In the picture we have compared the two models: the tool holder on the left has Uneven Flange Cuts, while in the second tool holder the cuts are similar and therefore we say it’s a tool holder with Identical Flange Cuts.

Tool Holder Cuts In Flanges Amastone

Tool Fitting

While the pull stud, body, and flanges depend on the machine, the lower part of the tool holding the fitting depends only on the application.
In the marble and glass sector we have mainly four different tool fittings:

1. ER collet holder
2. 1⁄2 “ GAS fitting
3. Profile wheels fitting
4. Stubbing wheels fitting

In the photo, you can see four cones with different fittings.

Tool Holders Flanges Amastone

Clamping Systems

Even if it is not a part that makes up the CNC tool holder, the clamping system deserves attention because it is a very important component that is inside the electrospindle and enables the attachment of the tool holder to the machine. They allow the automatic locking of tool holders.

For the ISO and BT CNC tool holders, we have mainly two types of clamps that depend on the type of pull stud that can be “angled” or “radius”. For the HSK we have a different type of clamping system that we will call HSK Clamp.

In detail we have:
Petal Collet: for hooking pull studs for both ISO and BT CNC tool holders. To identify a petal collet it is enough to know what type of ISO / BT the tool holder is; we need to know if the pull stud is angled or radius; and we need to measure the length of the pin. With this information, you can identify the correct petal collet in 90% of cases.

Ball Bearing Clamping Systems: for hooking a radiused pull stud in both ISO and BT. To identify the ball bearing clamping system it is necessary to know the type of electrospindle and pull stud.

HSK Clamps: for HSK CNC tool holders that, as we saw, do not have a pull stud. They, therefore, need a different hooking system.

Cnc Clamping System For Tool Holders Amastone

The materials

We can have CNC tool holders in three different versions:

1. Nickel-plated
2. Stainless Steel (Endurance Line)
3. Blacks (Darkside Line)

The nickel-plated version of tool holder cones (the first cone in the photo starting from the left) has been slowly abandoned over the last few years. The nickel-plated tool holder has the disadvantage that if it is splintered it corrodes easily. In fact, any damaged part is subject to corrosion because nickel-plating is only a surface treatment. However, some major manufacturers (such as Breton) continue to supply nickel-plated cones as standard with their machines.

Stainless steel tool holders are top of the range and are recommended for all users of CNC machines that are looking for high quality. It’s proved that the CNC tool holders with stainless steel bodies last longer. Even after many years (3- 4 years) of high usage, these tool holders do not lose tolerances and their concentricity. All this, however, is guaranteed if you perform good and constant maintenance. Also, IMS has developed the innovative “Endurance” treatment, a particular surface finish that allows an even smoother surface on which water and dust glide off. This increases the protection of the product against rust but the endurance treatment is NOT available for HSK CNC tool holders.

A good alternative to stainless steel is the black tool holder cones in the “Darkside” version of IMS, which requires minimal maintenance. Easily recognizable by their black color, these CNC Tool holders are heat-treated cones that guarantee a high level of protection against rust. After long use, they may lose some tolerance and will need replacing. The Darkside cones are also the cheapest line when compared to the same model with the Inox or nickel-plated tools.

Materials For Tool Holders Inox Nichel Darkside


It would be nice to have a unique code that identifies any CNC tool holder, explaining the family, the type of pull stud and the type of tool fitting without any margin of error. But unfortunately, it is not like this!

Across the marble, glass, wood and mechanical sectors there are many types of CNC tool holders and the identification of the correct tool for a specific machine is not always simple. The confusion is due to the fact that the machine makers do not follow the standards as they are defined but they change the tools for technical, or often commercial, reasons.

The “customizations” can involve the flanges that fit the tool forks, the cuts in the flanges, the pull stud or something else. Each tool holder presents a series of elements and variations (from the standards) that personalize the tool of a specific manufacturer. If we focus for example on the marble and glass sector we can say that a Bavelloni tool holder cannot work on a Brembana machine, or that a tool holder from a GMM saw would not be good for a Thibaut machine. To identify the type of the CNC tool holder we often need to know the industry sector, machine manufacturer, spindle brand, application and type of tool to be used.

Customizations in the marble and glass industries

In our specific sector we can state that:

• Intermac mainly uses ISO 40 CNC tool holders with side cuts and double flanges with radius pull stud and so we will find a ball bearing clamping system.

• Breton uses mainly ISO 40 CNC tool holders with identical cuts and HSK 80 B tools with an internal unit. The internal unit consists of a pin with a washer and an OR and serves to pass water through the axle and clamp. Breton tool holders are always nickel-plated.

• Denver, Helios and Thibaut use mainly BT CNC tool holders with BT pull studs or a customized one. For example, the helios’s pull stud has an OR inside.

• Brembana uses mainly ISO tool holders without cuts in the flange. The pull stud in Brembana CNC machines is a DIN 69872

• Oma mainly when it mounts ISO 50, follows the DIN standard with uneven cuts and with a tooth.

• VEM is mainly equipped with BT tool holders with BT pull stud.


Good maintenance, both of the tool holder and of the seat inside the electrospindle, gives the tool holder a longer life and the machine works better and more efficiently.

Always check the CNC tool holder at the end of each process, do not leave them assembled and clean them by drying with a dry cloth to avoid surface corrosions. Once you’ve removed the tool holders, check the pull studs and replace any damaged, chipped or corroded ones.

Do not forget to clean the seat in the spindle with the special Spindle Cleaner in order to remove any dirt that will inevitably be created during the work.

We also recommend a periodic checking of the clamping system (petal collet or ball bearing clamping system). The clamping system is subject to wear because it works under high mechanical stress and therefore must not be neglected. For this reason, we always recommend having an extra petal

collet as a spare to avoid long downtime in case of an unexpected break of the clamp.

WARNING: an abnormal vibration of the tools can be an alarm bell regarding the status of the clamp. Replacing the petal collet unit on ISO and BT tool holders is very simple, you just need an allen wrench to unscrew a screw. It is a bit more complicated to replace a clamp in the HSK tool holders. For this, the HSK clamps are supplied as a kit together with a special key and instructions to follow.

Through the amastone e-commerce site, we supply CNC tool holders worldwide on a daily basis to customers operating in different sectors, not just marble and glass. Thanks to our close collaboration with IMS we benefit from the experience of one of the most important Italian manufacturers. For this reason, we can satisfy even the most complicated requests with speed.

We can assist with all problems discussed in this article before and after you make your purchase. Our technicians will ask you to verify your tool holders through a photo or through additional information on your CNC machine and electro-spindle. With this information, we can help you keep errors down to an absolute minimum.

By the amastone e-commerce site, we daily supply tool holders worldwide to customers operating in different sectors, not just marble and glass. Thanks to the close collaboration with IMS we join the experience of one of the most important Italian manufacturers and for this reason, we can satisfy even the most complicated requests with speed.

Precisely for the problems discussed in this article during the pre-sale phase, or immediately after receiving direct orders online, it is possible that our technicians ask to verify the correctness of the CNC tool holders through a photo or through additional information on the CNC machine and on electro-spindle. Through the photo of a used tool, or of a pull stud, or knowing the model of the machine we reduce to the minimum any possibility of error.

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2 thoughts on “CNC Tool Holders in the Marble and Glass Industry

  1. Kendall Gosvener says:

    I am working on a CTEC-4 machine and I am trying to figure out if a G-40 conical tool holder is the same as a ISO 40 tool holder. The machine is a stone cutting CNC, and we need to purchase some tool holders but want to make sure we purchase the correct tool holder for the machine.

    1. Marco Divita says:

      Hi Kendall,
      no problem, to select the right tool holders please send me a photo of the one that you have and a photo of its pull stud.
      Send me the photos via email at

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