Question

the fastening device pictured below is: toggle bolt machine screw hex - headed bolt carriage bolt

Explanation:

The fastener in the image has a rounded head and a square section under the head, which are characteristic features of a carriage bolt. A toggle bolt is used for fastening in hollow walls, a machine screw has a flat or recessed head for driving with a tool (like a screwdriver), and a hex - headed bolt has a six - sided head. The given fastener does not match these descriptions. The carriage bolt's design (rounded head and square section) is for applications where a smooth, rounded appearance is desired on one side (the head side) and it can be prevented from turning during tightening (due to the square section).

Answer:

Carriage bolt