An anchor (910) for mounting to a hollow wall (W) made of friable material comprises a proximal flanged end (918) adapted to be engaged by a rotatable tool (B) to rotate the anchor (910) about a longitudinal axis (A) thereof and to cause is to gradually engage the wall (W). The anchor (910) also includes a distal end (912) adapted to cut through the wall (W) as the anchor (910) is rotated, and a shank (920) extending between the proximal and distal ends (918, 912). The shank (920) includes at least one expandable leg (924) that is in a collapsed position thereof when the anchor (910) is rotated to mount it to the wall (W) and that is located distally beyond a non visible surface of the wall (W) once the anchor (910) has been mounted to the wall and is in a first position thereof. The wall anchor (910) includes an outer thread (922) that securely engages the wall (W). A threaded fastener (B), e.g. a screw, is adapted to be introduced in the anchor (910) and to threadably engage the same distally of the leg (924) such that sufficient rotation of the threaded fastener (B) retracts the distal end (912) towards the proximal end (918) thereby causing the leg (924) to displace to a laterally expanded position thereof and to engage the non visible surface of the wall (W).