Abstract: A fastener can be inserted into a narrow space behind a wall, and can be brought into contact with the back of the wall over a wide area to sufficiently reinforce the wall even when a bolt is tightened to securely fasten an object to the wall. The fastener has a block assembly including a plurality of blocks having two longitudinal ends and coupled together at the longitudinal ends in a single line. One of the blocks is formed with a threaded hole into which a bolt is adapted to be threaded and string holes. At least one string member is passed through the string holes. The block assembly has an arrangement for preventing each block from pivoting in a first direction from a straight position, in which the block assembly is arranged in a straight line, and allowing each block to pivot in a second direction opposite to the first direction from the straight position.