The anchor which is suitable for location in semi-solid or particulate material has a body portion (10) to which pivotal vanes (15) are attached. The vanes (15) are arranged to lie in a first position adjacent the body portion (10) when the device is being driven into an anchoring region and to pivot outwardly in a direction away from the body portion (10) when the device has been caused to penetrate the anchoring region to a required extent. Outward pivoting of the vanes (15) may be effected by turning the anchor when it has penetrated into the anchoring region. When the vanes (15) lie in the first position the device presents a minimum area of resistance to penetration into the anchoring region, and when the vanes lie in the second position the device presents a maximum effective area of resistance to extraction of the anchor. <IMAGE>
