Abstract: A coil spring having fixedly attached washer members at each end encircles a mine roof bolt and is retained between radially projecting ears on the bolt and an expansion anchor threaded on the bolt. The washer member which engages the bolt ears is slotted to receive the ears so that rotation of the bolt is transmitted to the spring and the other washer member. The washer member at the other end has a pair of stepped shoulders on the face opposite the spring which engages the lower end of the anchor shell. The latter is also provided with a pair of stepped shoulders which cooperate with those on the washer member to transmit rotation from the bolt to the anchor in one direction and allow relative rotation in the other. In this manner, a resin grouting cartridge placed in the drill hole ahead of the anchor may be broken and its contents mixed by rotation of the bolt and anchor as a common unit, and the anchor expanded to tension the bolt as the resin sets by rotation in the opposite direction.