One size 18 1/2 silicone sac, made from 100% silicone. These sacs will not break down or release any sulfur compounds as it ages. Ideal for celluloid pens with excellent color. Please note: Price is per sac. Pen sacs are measured in 64ths of an inch diameter. Most sacs will need to be trimmed prior to use and are intentionally made longer than necessary.