Roller Blind Chain Drive with Idler& Brackets- Acmeda- 32mmMeasure the diameter (distance across the tube, not around) of the tube to work out the size. Measurement needs to be taken from the inside edge of the inside of the tube. Australian sized tubes generally come in 3 sizes 32mm, 38mm, 43mm.
The internal diameter that fits a 32mm chaindrive will be APPROX 31mm
Available Colours- 32mm -White, Black, Cream