A tanren bō (鍛錬棒) is a bat used in aikido for strength and suburi training. Despite being only 3 feet (0.91 m) overall, with 10 inches for the handle, the "blade" is a large lump of rectangular wood, with its cross-section being a square with dimension of three square inches, and has an overall weight of 4 to 7 lbs.
By designating one corner as edge, an aikidoka can use it as an even heavier suburitō, practice suburi, kata, hasuji (edge-angle) and tomei (swing stopping), and learn the bounce-back of the sword by practising against tanrenuchi, now typically a tyre stood upright on a concrete base.
As it is designed towards aikido and strength training, specifically for getting used to the weight of a heavy-handled object, it does not resemble a sword in shape, length, or mass. Thus, unlike suburito, it is less effective for learning the katana's cut, and is not suited for contact with other swords.