There are two types of self-retaining bolts. What are they?

• A. Impedance and Positive retention
• B. Twin-thread and single-thread
• C. Negative retention and Self-locking
• D. Quick-release and Permanent

Answer: (A)

Self-retaining bolts stay in place by using two different retention methods. One method is impedance, which provides resistance to loosening through the fit and friction between the bolt and its mating surface. The other method is positive retention, where a locking feature actively prevents the bolt from backing out, such as a locking groove or washer that grabs the bolt when installed. Together, these cover a passive approach (friction/fit) and an active approach (locking mechanism) to keep the bolt secure under vibration and loads. The other options mix up thread types or release characteristics rather than describing the retention mechanisms these bolts use.