A fastener comprising a cylindrical member connected to a first strap section along the cylinder's wall, a tube-shaped member connected to a second strap section along the tube's wall. The tube has an opening within its wall to allow the passage of the first strap therethrough, and may comprise a display window covered with a magnifying glass to allow the assessment of the relative tension between the two opposing straps. The first strap section is attached to the second strap section by inserting the cylinder in the tube. The fastener is adapted to be brought to a fastened state in which the first strap and second strap are connected via the fastener at a desired tension and an unfastened state in which the first strap and second strap are separated