These wall or ceiling mounting clamps (also known as fairleads) are a useful accessory to clip your lighting flex to fat surfaces.
They have a hidden screw hole for invisible fixing to walls, ceilings, beams or pillars.
The top section then unscrews, the cable fits in the gap and the top then screws down onto the flex, enough to prevent movement and hold the flex taut but not enough to cause damage.
There's a huge amount of ways to use these, create visual impact by routing cables in an angular route across walls or ceilings. Run multiple cables parallel to each other or create straight cable runs without sagging across light wells or other openings.