I first used normal curtain rails 25mm that were galvanized but they did not work very nice. I finally found a place that sells 25mm stainless steel smooth rods and it made a huge difference on my side. I used my caliper now to check the dimensions and it measures as follows: 25.4mm Outer Diameter with 1.5mm thick walls meaning a Inner Diameter of 22.4mm . Funny enough, the stainless steel was way cheaper then the curtain rails. The machine runs much smoother with the stainless steel.