The premium shells vary from approx. 9-10 mm on the 20" and the shells are high quality like the one shown on that selection. The natural varieties are approx. 18" 20" or 24" in length and the shells on most are in the 9-11 MM size. If you would like to see what you will receive for these, please ask and we?ll send a photo. We string these here on Maui with real puka shells sourced from the Philippines, so no two are alike. We highly recommend asking for a photo of the item you will receive prior to purchasing if you have any questions. They are priced by the quality of the shells. Twist-Barrel clasp.The word "puka" means "hole" in the Hawaiian language, which in the case of these necklaces refers to the naturally occurring hole that is found in pieces of shells. Packaged in a drawstring pouch for giving. Could also be taken apart to use shells for other craft projects. If you don't see what you're looking for here, please ask, we have many other styles, colors and shell leis and bracelets available. If you need larger quantities, please ask.ease ask.