Velcro hooks. Coloured scanning electron micrograph (SEM) of fastened velcro. Velcro is a two-sheet material which is used as a reversible fastener on clothing and fabrics. One sheet consists of hooks (pink), the other of loops (brown). When the two sheets are pressed together, the hooks attach to the loops, giving a secure grip but one that can be easily undone. Magnification: x15 at 6x7cm size.