A steel tongue drum can be made from an empty (often 20 lb) propane tank. The tank is flipped over, the base cut/knocked off; and seven to ten tongues are cut radially into the bottom of the tank, forming the top of the instrument. Steel tongue drum can also be made from new unused tank heads. The tongues can be tuned by the maker by varying the length of the cuts, or by adding weights, often neodymium magnets to the tongues. The steel tongue drum is often tuned to pentatonic scales but can be tuned to the diatonic scale, the chromatic scale, or any set of notes the maker chooses. The instrument is played with the fingers or with mallets. The tone is bell-like. The steel tongue drum had several predecessors, most notably the Whale Drum by Jim Doble and the Tambiro by Felle Vega. In February 2007 Dennis Havlena, inspired by the physical properties of the Tambiro and the tone layout of the Hang, created a steel tongue drum with a circular cross pattern layout and from an empty 20-pound propane tank. The name 'Hank Drum' came from a combination of "Hang" and "tank". Dennis Havlena's instrument, in turn, has inspired other steel tongue drum inventions. Today there are a lot of vendors of commercial versions of the steel tongue drum worldwide