Recommended for secondary piercings; Uses a 0.04 inch (0.9 mm) post. 18K gold stud earrings that are nickel free and friendly for those with metal allergies; Size: Round ball 0.16 inch (4 mm), Post length 0.4 inch (10 mm), Post diameter 0.04 inch (0.9 mm); Material: K18 gold (nickel-free so it is safe for those with metal allergies); Recommended for beginners.