The inside diameter of our eyelets is 40mm. This means that a wide range of curtain rod thicknesses will fit. The diameter of standard curtain rods is often between 16mm and 28mm and all of these diameters will fit. Please note that the larger the diameter of the rod, the less the eyelet can tilt when the curtain is moved. Very large diameters will therefore require more material to cover an area than smaller diameters. We therefore recommend that you choose rods no larger than 30mm in diameter.