Abstract: A tumbler for tumbling concrete products comprises a rotatable cylindrical drum having an input end that is slightly elevated relative to an output end. Tire retread strips are placed side-by-side on the radially inner surface of the drum and extend along its length. Clamps having lateral arms extending on either side are engaged with lateral tread grooves on the strips. The clamps are bolted to the drum between adjacent strips thereby securing the strips to the radially inner surface of the drum.