Appearance: scar or uneven, depth or height shall not exceed the thickness of the pad tolerance;
Bubbles: per square meter, the area is not less than 1cm2 bubbles no more than 5, the distance between any two bubbles is not less than 40mm;
Impurities: depth and length does not exceed the thickness of the pad is not less than 40mm;
Uneven edge or sponge-like: the width of not more than 10mm, the length of not more than 1/10 the total length of the pad;
Crack: not allowed.