I would like to have enough coins to fill all these tubes! The educational value of their contents are enormous! I use the clear polystyrene tubes for sand samples and the polypropylene tubes for microfossil fill. The caps fit snugly and securely, the will hold about 30 ml of material, and they ship without accidents! That's the study application! The other functions are limited only by what you can get into them! Thanks for a uniform, quality product!