20a and an expansion element 20b which can be axially displaced through the sleeve however when initially placed within the guide member the anchor is in its unexpanded condition when the expansion anchor is loaded into the guide member it is possible that it could be accidentally displaced through the front end of the guide member accordingly a retaining means 21 in the form of a ball catch is provided extending into the bore forwardly of the position of the expansion anchor as shown in fig1 the ball catch 21 consists of a spring biased ball seated within a recess in the guide member with the biasing action causing the ball to project into the path of the expansion anchor if the combination of the magazine 6 and the guide member 4 is pushed rearwardly the piston sleeve 3 is also moved in the rearward direction due to the friction contact produced by the spring 17 until the front end of the slot 18 in the sleeve strikes against the stop member 15 by further rearward movement of the combined magazine 6 and guide member 4 the expansion anchor 20 is partly ejected by the piston assembly from the front end of the guide member until a stop pin 22 mounted in the housing moves into the engaged position with the.