15 Shell Hermit Crab Changing Shell Pack (HCS1801) Sizes range from 3/4″-2″ Overall Size Opening Sizes are 3/8″-1 1/4″ (all sizes are approximate) Hermit Crabs need an assortment of Seashells as they grow. This set is perfect for very small to medium size Hermit Crabs You will receive shells similar the the ones in the pictures – Substitutions are possible. Hermit Crab Changing Shell Set (small to medium) For Small to Medium Size Hermit Crabs Opening sizes range from 9-31 mm Great as Aquarium Decor Plenty of shells for small Hermit Crabs to grow into