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The Differences Between BT, SK, ISO, PSC & HSK Toolholders


There are lots of things to consider when looking to purchase the right tool holder for your application.

Over the years we have been asked all sorts of questions from customers who have varying levels of knowledge and experience. I have summarised below some of the most frequently asked questions that I am asked on a regular basis...


What are the main differences between each taper?

There are different types of tool holder tapers because they are designed to be compatible with different types of machine tools and cutting applications. Different machine tools may have different spindle tapers, which determine the type of tool holder that can be used. Additionally, different types of cutting tools, such as end mills, drills, and taps, may require different types of tool holders to correctly secure them in the machine spindle.

Some common types of tool holder tapers include BT, SK (DIN69871), ISO (DIN2080), HSK and PSC (Polygon Shank). The choice of tool holder taper depends on the specific application and machine tool being used and it's important to select the appropriate taper to ensure compatibility and reliable performance.


Typically, what machines do they go on?

  • BT (also known as BT MAS) tool holders are typically used on Japanese, Korean, Taiwanese, and American machine centres.
  • SK (also known as DIN69871) tapers are used on German and European machining centres, these can also be used on American machining centres taking CAT40/CAT50 tooling.
  • ISO (also known as DIN2080) tool holders are typically used on conventional (manual) milling machines with manual or automatic draw bars.
  • HSK (also known as DIN69873) tool holders are primarily used on high-speed CNC machining centers, particularly those with spindle speeds of 10,000 RPM or higher. HSK tapers were developed in Germany and have become popular in Europe and other parts of the world for their excellent performance in high-speed machining applications. HSK tapers have a hollow shank design that provides a more direct and efficient transmission of power to the cutting tool, resulting in better accuracy, stability, and cutting performance.
  • PSC (Capto compatible) tool holders are ideal for CNC machines. They are designed to hold cutting tools with polygonal shanks, which provide improved tool grip and stability during machining operations.

 BT (also known as BT MAS) tool holders are typically used on Japanese, Korean, Taiwanese, and American machine centres. 

  •  SK (also known as DIN69871)  tapers are used on German and European machining centres, these can also be used on American machining centres taking CAT40/CAT50 tooling.

  •  ISO (also known as DIN2080) tool holders are typically used on conventional (manual) milling machines with manual or automatic draw bars.

  •  HSK (also known as DIN69873) tool holders are primarily used on high-speed CNC machining centers, particularly those with spindle speeds of 10,000 RPM or higher. HSK tapers were developed in Germany and have become popular in Europe and other parts of the world for their excellent performance in high-speed machining applications. HSK tapers have a hollow shank design that provides a more direct and efficient transmission of power to the cutting tool, resulting in better accuracy, stability, and cutting performance.

  •  PSC (Capto compatible) tool holders are ideal for CNC machines. They are designed to hold cutting tools with polygonal shanks, which provide improved tool grip and stability during machining operations.


  • How are they clamped into the machine and why?

    BT, SK and ISO tool holders have something called a steep taper. These are typically clamped into the machine via the use of a drawbar inside the spindle that clamps the pull stud located in the back of the taper. Steep taper tool holders tend to be a more conventional approach and can lose accuracy when running at extremely high RPM’s. These also tend to have a taper ratio of 1:10.

    HSK tapers (German abbreviation for hollow taper shank) on the other hand are classed as dual contact, meaning it maintains contact on the spindle taper and flange on the spindle face to create a solid connection both axially and radially. This creates a resistance to axial movement and prevents the holder from being pulled about making it ideal for higher speeds. HSK holders have a taper ratio of 7:24 and are also available in different types such as HSK-A, HSK-C, HSK- E and HSK-F. The main reason for different types of HSK tapers are dependent on the speed or torque requirements.


    What type of outputs are available on each type?

    BT, SK and HSK tapers are the most commonly used in the UK manufacturing industry. Therefore there is usually a comprehensive range available for these options. Meaning all general performance options are covered such as side lock holders, collet chucks and face mill arbors but also higher performing holders such as hydraulic and shrink chucks.

    ISO (DIN2080) holders are slightly old fashioned nowadays and therefore you will generally only find the more conventional options available such as side lock arbors and collect chucks. This is in no small part down to the spindle speed limitations of DIN2080 machines which would make the use of higher speed holders unfeasible.

    Finally PSC (capto compatible) holders are available for both CNC milling and turning machines. Traditional milling holders include ER collet chucks, side lock arbors and face mill arbors whilst turning holders include boring bars, turning tools and thread turning holders.

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