This is an authentic replacement pyrex glass tank with a hollowed-out stainless steel sleeve for the Aspire Nautilus Tank. Aspire’s clever design features a glass tank with a webbed stainless steel sleeve surrounding it. Eliminating the top and upper tube reduces the number of places the product could potentially unscrew and leak. The hollowed-out sleeve will replace the glass tank and the top cap on your original Nautilus tank. The Nautilus hollowed-out sleeve by Aspire is a beautiful and functional piece of art.