The initial is silver plated and measures 10 mm x 15 mm. It is strung on a silver plated tiny 1.3 mm curb chain with a lobster clasp closure. Choose the length from the drop down. To add a birthstone charm to this necklace, follow link below to purchase birthstone charm. https://www.etsy.com/listing/634099372/add-a-birthstone-charm?ref=shop_home_active_1