Please note the backs in the picture are magnified to show colours. The disc measures 6mm. Replacements for Studex Sensitive and Studex Tiny Tip Range. Not suitable for Studex Plus earrings. 100% Hypo-allergenic. Gauge/Thickness: 0.8mm (20 gauge). Pair of replacement butterfly backs for earrings with posts up to 0.8mm / 20 gauge. Butterfly backs hold earrings securely in place. Studex are ideal for everyday use especially if you have sensitive ears. Each classic pair is made of the highest quality surgical stainless steel and 9 karat gold plated. Each style is safe enough to be worn every day, guaranteed.