This is a specially designed Thatukali/Thattu Mannai by JAS technicians, toproduce rhythm in theperformance of Bharathanatyam dance; It has double grooves and pin holes at the corners whichallow sound to resonate better without hitting hard on the block and the tone producedis musical rather than a dry bang sound of a conventional solid Thatukali/Thattu Mannai. Rhythm is called Nattuvangam, Person who produces theRhythm called Nattuvanar. Instruments used are called NattuvangamThattukali/Thattu Mannai and Nattuvanga Thalam