Final answer:
A hex bolt or hex screw is the type of fastener that requires a hex driver, which is also known as an Allen wrench, to be tightened or loosened by turning it clockwise or counterclockwise respectively.
Step-by-step explanation:
The type of fastener that is loosened and tightened with a hex driver is commonly known as a hex bolt or hex screw. A hex driver, sometimes called an Allen wrench or a hex key, is an L-shaped tool used to drive bolts and screws with a hexagonal socket in the head. To use a hex driver, you insert the tool into the hex slot of the fastener and turn it clockwise to tighten or counterclockwise to loosen.