Just go to the craft store and purchase a bag of empty shells. There usually only a couple of bucks. You need to boil them to disinfect before putting them in the tank. The ones marked especially for hermits are usually alot more expensive. I read that hermits like more round openings as opposed to slits and this seems to be true with mine. Put a variety of shells in the tank for your crab to choose from. Also, the 1/2 inch is referring to the size of the opening on the shell.