How to Identify Your Roller Blind Mechanism & Tube Size
Updated: Aug 11
If your roller blind mechanism has broken or become difficult to operate, replacing the mechanism can often be much cheaper and easier than replacing the complete blind.
The important part is identifying the correct replacement.
Roller blind mechanisms come in different sizes and designs, and a mechanism that looks similar may not necessarily fit your existing roller tube.
In this guide, we'll explain how to identify your roller blind tube size, operating mechanism and fittings before ordering replacement parts.
Step 1: Identify How Your Roller Blind Operates
Start by identifying the type of mechanism fitted to your blind.
Most domestic roller blinds use one of two systems:
Chain-operated mechanism, often called a sidewinder
Spring-operated mechanism, where the blind is raised and lowered without an operating chain
A chain-operated roller blind normally has a plastic or metal chain loop running through a mechanism at one end of the roller tube.
A spring roller blind contains a spring mechanism inside the tube and is operated by pulling the blind itself rather than using a chain.
If an old spring mechanism has failed and a suitable replacement isn't available, it may also be possible to convert a spring roller blind to chain operation rather than replacing the complete blind.
Step 2: Measure the Roller Blind Tube Diameter
One of the most important measurements when identifying a replacement mechanism is the outside diameter of the roller tube.
Don't measure the hole inside the tube.
Measure straight across the outside of the tube from one edge to the other, preferably with the blind removed so you can measure accurately.
Common roller blind tube sizes include:
Tube Size | Typical Use |
25mm | Smaller and older roller blind systems |
28mm | Common domestic and DIY roller blinds |
32mm | Very common domestic and made-to-measure roller blinds |
40mm | Larger/heavier roller blind systems |
These aren't the only roller tube sizes ever manufactured, so don't assume your blind must be one of these.
The important thing is to measure the tube you actually have.
Step 3: Don't Guess the Tube Size From the Blind Size
A common mistake is assuming that the physical width of the blind tells you the diameter of the roller tube.
It doesn't.
A wider blind may use a larger tube to provide additional strength, but different manufacturers and systems use different tube sizes.
Two roller blinds of a similar width could therefore have different diameter tubes.
Always measure the actual tube before ordering a replacement mechanism.
Step 4: Check the Tube Profile
Tube diameter isn't the only thing that matters.
Look carefully at the profile and shape of the roller tube, particularly at the open end where the mechanism fits.
Many roller blind tubes are slotted to allow the blind fabric to be attached to the tube.
The internal profile also determines how the mechanism fits into the tube.
A replacement mechanism therefore needs to be compatible with both the diameter and profile of your existing tube.
Step 5: Remove and Examine the Existing Mechanism
If possible, remove the blind from its brackets and carefully examine both ends.
On a chain-operated roller blind you will normally find:
The control mechanism or sidewinder at the chain end
An idle end or pin end at the opposite end
Look at how these components fit into the roller tube.
Useful things to check include:
Overall mechanism size
Shape of the section inserted into the tube
Tube diameter
Shape of the bracket fitting
Pin or idle-end design
Chain size and type
Taking a few photographs before dismantling anything is a very good idea.
They give you something to refer back to and can also be useful if you need help identifying the replacement.
Step 6: Check the Roller Blind Brackets
Don't forget about the brackets.
Different roller blind mechanisms can use different bracket designs, so your existing brackets won't necessarily be compatible with a replacement mechanism.
Fortunately, many replacement roller blind mechanism sets are supplied with the appropriate control mechanism, idle end and brackets.
This means you don't always have to find a mechanism that fits your old brackets exactly.
If you replace the complete mechanism set, the new brackets can often be fitted in approximately the same position as the existing ones.
Step 7: Do I Need Exactly the Same Brand?
Not necessarily.
If you can obtain an identical replacement mechanism, that can make the repair particularly straightforward.
However, the original manufacturer or mechanism may no longer be available, particularly on an older blind.
In many cases, what's more important is finding a replacement system that is compatible with the existing roller tube.
This is why tube diameter, profile and fittings are more useful than simply trying to identify a brand name.
What If My Roller Blind Mechanism Is Very Old?
Don't automatically assume that an older roller blind can't be repaired.
Mechanisms for older and smaller tube sizes, including some 25mm and 28mm systems, are still available.
If an exact replacement isn't available, there may also be other options.
For example, an older spring-operated blind may sometimes be converted to a modern chain-operated mechanism while retaining the existing fabric and tube.
In other cases, it may be possible to upgrade the blind to a newer tube and mechanism system.
The more components that need replacing, however, the more important it becomes to compare the cost of the repair with replacing the complete blind.
What Size Roller Blind Mechanism Do I Need?
As a quick checklist, identify the following before ordering:
Check | What to Look For |
Operation | Chain or spring |
Tube diameter | 25mm, 28mm, 32mm, 40mm or another size |
Tube profile | Shape and internal fitting |
Control end | Sidewinder or spring mechanism |
Idle end | Pin/end fitting |
Brackets | Existing type or replacement brackets |
Chain | Plastic/metal and compatible bead size |
Old parts | Keep them and take photographs |
If you can establish these points, identifying the correct replacement becomes much easier.
Can I Change to a Different Size Roller Blind Mechanism?
You can't normally fit, for example, a 32mm mechanism directly into a 28mm tube simply because you prefer the larger mechanism.
The mechanism needs to be designed for the tube.
However, you can potentially upgrade the complete tube and mechanism system.
For example, an older blind could sometimes be converted to a modern 32mm system by replacing the tube as well as the operating mechanism.
Whether this is worthwhile depends on how much of the existing blind needs replacing.
If the fabric is still in excellent condition, upgrading the hardware can sometimes make sense. If the tube, mechanism and several other components all need replacing, it may be time to consider whether a complete new blind would be more economical.
Do I Need to Replace the Fabric?
Usually not.
If you're replacing a compatible mechanism while retaining the existing roller tube, the blind fabric can normally remain exactly as it is.
There's usually no need to cut the fabric or change the width of the blind simply because the operating mechanism has failed.
That's why replacing a mechanism can be such an economical repair.
A perfectly good blind doesn't necessarily need replacing just because one relatively small component has worn out.
Still Not Sure Which Roller Blind Mechanism You Need?
If you're still unsure, don't guess.
Measure the outside diameter of the roller tube, take clear photographs of the mechanism, tube ends and brackets, and compare them carefully with the available replacement parts.
You can browse our Roller Blind Mechanisms to compare replacement mechanisms for common roller tube sizes.
For other roller blind faults and repair advice, visit our Roller Blind Repairs & Guides section.
Conclusion
Identifying a roller blind mechanism is much easier once you know what to look for.
Start with the operating type and outside diameter of the roller tube, then check the tube profile, mechanism ends and brackets.
Remember:
Measure the tube – don't guess from the size of the blind.
A little time spent identifying the existing system can prevent ordering the wrong part and, in many cases, a relatively inexpensive replacement mechanism can keep an otherwise perfectly good roller blind working for years to come.
If you wish to change how your Roller Blind operates, see our article "Roller Blind chain vs spring operation"
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