HIGH QUALITY - This rock polisher grit refill pack comes with enough high-quality silicon carbide grit to put a dazzling polish on up to 20 lbs. of rocks, gems, glass, and more! EASY TO USE, FOUR-STAGE ROCK GRIT - The first rock tumbling grit stage provides initial shaping, the second smooths rock surfaces, the third pre-polishes rocks, and the fourth provides the final polish! COMPATIBLE WITH ALL TUMBLERS - This complete 4-step rock tumbler grit refill kit works with all rock tumblers. For best results, use with National Geographic Rock Tumblers and rock tumbling supplies. EASY TO MEASURE AND STORE - Each rock tumbling grit stage is packaged in a wide-mouth container with secure, screw-top closure. AWARD-WINNING PRODUCTS - Blue Marble, winner of the Toy Association's prestigious Toy of the Year Award, proudly develops products that foster education, imagination, and creativity, with a U.S. support team to ensure a stellar experience!