How to Attach Castors to Round or Square Tubing

Attaching castors to round or square tubing is a common requirement for trolleys, equipment frames, furniture, and industrial workstations. Using the correct tube adaptor ensures the castor is securely mounted, allowing smooth mobility while protecting the structure of the tubing.

In this guide, we explain how tube adaptors work, how to choose the right adaptor, and the correct installation process for both round and square tubular frames.

Why Use Tube Adaptors for Castors?

When installing castors onto tubular frames, it is usually not possible to attach them directly to the open tube. Tube adaptors solve this problem by creating a secure fixing point inside the tube holding the castor securely in place.

Tube adaptors allow you to:

Securely mount castors into hollow tubing
Prevent tube deformation or damage
Convert tubular frames into mobile equipment

Most castor tube adaptors use an expanding mechanism. When the bolt is tightened, the adaptor expands inside the tube and grips the internal walls to create a strong, secure and stable fixing.

This method is commonly used for trolleys, carts, workbenches, laboratory equipment, furniture and display stands built with tubular frames.

Explore the range of Castors that suit the adaptor range

Bolt Hole Light Duty Castors 310 Series

Industrial Bolt Hole Castors 4000 Series

Twin Wheel Bolt Hole Castors 360 Series

Step-by-Step Guide to Installing Castors into Tubing

Step 1 – Measure the Tube Internal Diameter

Before selecting an adaptor, measure the internal diameter of your tube.

For round tubes, measure the internal diameter of the circular opening.
For square tubes, measure the internal width of the square profile.

Choosing the correct size adaptor is essential to ensure the expander grips the tube properly. Tube adaptors are designed to match specific internal diameter ranges.

Step 2 – Select the Right Tube Adaptor

Round tube adaptors are designed to fit inside cylindrical tubing. These adaptors expand evenly around the tube interior when tightened, creating a strong internal grip.

They are commonly used for:

Equipment frames with round legs
Light- to medium-duty trolleys
Stainless steel tubular structures

Choose a round adaptor that matches your tube's internal diameter range.

Example internal diameter sizes include: 18–19.5 mm, 19.5–21.7 mm, 21.7–24.5 mm, 24.5–27 mm, 27–29.5 mm, 29.5–32 mm

Step 3 - Secure adaptor to the castor via the bolt hole opening

Once you have selected the correct adaptor: Insert the adaptor bolt into the castor bolt hole section. So you are now left with a castor and adaptor attached together as one secure unit.

Step 4 – Insert the attached Adaptor into the Tube

Insert the adaptor into the tube, and tighten the allen key head. As this tightens, the adaptor expands inside the tube, gripping the internal walls and locking the castor into place.

This expanding mechanism eliminates the need for welding or drilling.

Step 5 – Test the Installation

After installation:

Check the castor rotates smoothly
Ensure there is no movement or wobbling
Confirm the assembly supports the intended load

Properly installed tube adaptors create a secure and professional finish, allowing equipment to move safely and reliably.

Frequently Asked Questions (FAQ)

Q: Can castors be attached directly to round or square tubing?

A: By using an adaptor which means there is no need for welding or drilling. Most tubular frames require a tube adaptor to create a secure fixing point inside the tube. The adaptor expands within the tube when tightened, holding the castor firmly in place.

Q: How do I know which tube adaptor size I need?

A: To choose the correct adaptor, measure the internal diameter of the tubing.

For round tubing, measure the internal circular diameter.
For square tubing, measure the internal width of the square section.

Once measured, select a tube adaptor designed to fit within that size range to ensure a secure grip inside the tube.

Q: Are tube adaptors suitable for heavy-duty applications?

A: Yes. Tube adaptors are commonly used in industrial trolleys, workshop benches, storage racks, and equipment frames. When combined with the correct castor type and load rating, they provide a strong and reliable fixing for both light-duty and heavy-duty applications.

Q: Do tube adaptors work with all types of castors?

A: Tube adaptors are typically designed to work with bolt hole castors, such as the 4000 Series, 360 Series and 310 Series. It is important to ensure that the adaptor and castor fixing type are compatible. Ross Castors offers a range of adaptors that suit our bolt hole castors.

Q: Can tube adaptors be used with stainless steel castors?

A: Yes. There are tube adaptors suitable for use with stainless steel castors, including both round and square tubing options. These are often used in environments where hygiene or corrosion resistance is important, such as food production areas, laboratories, or medical equipment.