S40 Roller Blind Tube: How to Identify It & Which Motors Fit

If you have an older Australian roller blind, there is a good chance you may come across an Acmeda S40 T-Spline tube. It predates the modern S45 platform but can still be a very practical tube to retrofit when the profile is correctly identified and matched to the right motor adaptors.

How to identify an S40 tube

The S40 has an outside diameter of roughly 39.4mm and a distinctive T-Spline internal profile. The profile matters much more than whether someone casually calls it a 40mm tube. Remove the blind, take out the idler and compare the open tube end with a confirmed S40 image.

Where S40 tubes are usually found

S40 is commonly seen in older Acmeda roller blind systems and pre-RB09 installations. It was widely used on small and medium residential blinds and can remain perfectly serviceable years later, so replacing the entire blind solely because it is older is often unnecessary.

Can an S40 roller blind be motorised?

Yes, when the tube is a genuine compatible S40 profile and is in good condition. The chain mechanism is removed and the selected tubular motor is fitted using the correct S40 crown and drive arrangement. Because this is an older tube family, adaptor choice is especially important.

Use our current S40 compatible motor page rather than assuming a motor marketed for another 38–45mm tube will fit.

How big can an S40 blind be?

S40 was generally used on smaller to medium blinds, often around the 2.0–2.4 metre width range depending on fabric weight and drop. Treat that as a guide rather than a universal limit. A heavy sunscreen fabric and a light blockout fabric of the same width can create different loads.

S40 vs 38mm: do not choose by diameter alone

An S40 can sit close in diameter to other compact roller tubes, including some 38mm systems. The internal profile decides the adaptor. If you cannot clearly match the T-Spline shape, stop before ordering and identify the tube first.

Should you keep the S40 or replace it with S45?

If the S40 tube is straight, adequately rigid for the blind and has confirmed motor options, keeping it can make the retrofit simple. If it is damaged, undersized for a large blind or the rest of the hardware needs major changes, an S45 tube upgrade may be a cleaner long-term solution while retaining the existing fabric.

Not completely sure what you have? Start with the MMB roller blind tube identifier and compare the profile before choosing a motor.