Through-Shaft Design: What It Is and Why It Is Important

By Aimee O'Driscoll, 19 November 2019

When browsing stirrers, you may have come across some models that have a through-shaft design. We explain what this is and why it’s important.

A through-shaft design is one in which the position of the top of the shaft is less restricted; it can be inserted all the way through the stirrer head, providing a wide vertical range at which the impeller can be positioned. The shaft is inserted in the lower part of the unit, and goes through a collet which is typically tightened using a chuck key once the shaft is in place. Some newer models, such as certain Hei-Torque units that have a “Quick-Chuck” feature, don’t require a key.


Stirrers with a through-shaft design.

Left to right: The EUROSTAR 20, OS40 Overhead Stirrer, and Hei-Torque Value all have a through-shaft design.

There are a couple of benefits to using a stirrer with a through-shaft design:

  1. Adjusting the impeller is trivially simple. If you need to adjust the height of the impeller to any depth within your vessel, you have the freedom to move the impeller only, without having to adjust the entire stirrer unit. This is convenient and helps you avoid risks involved with adjusting the stirrer itself, such as accidentally dropping the unit and causing damage to the stirrer, your other equipment, or your sample. It’s especially helpful when dealing with heavier, more cumbersome units. 
  2. It offers more stability. It’s possible for shafts to vibrate when in use, and this can be more pronounced at high speeds or with long shaft lengths. The through-shaft design makes it easier to position the shaft with the impeller closer to the collet such that there is more stability and less susceptibility to vibrations.