Model: T157-2Material: IronColor: Red GreyExternal Diameter: approx. 40mmInside Diameter: approx. 24mmThickness: approx. 14.5mmInductance coefficient :AL 14nH/N2Permeability: 10μo approx.Reminder:1、 Magnetic rings are sold according to size, unit mm (mm), tolerance: + - 0-2mm2、 According to the size of the product description on the page, please don't just imagine buying out of thin air. If you don't understand, you can consult the customer service.3、 The magnetic ring is fragile. Be careful when using it. If you have any problems, please contact us for treatment.Due to the difference between different monitors, the picture may not reflect the actual color of the item. Thank you!