What type of nut is designed to fit into drilled holes and usually provides a self-locking feature?

The type of nut designed to fit into drilled holes and usually offers a self-locking feature is the channel nut. Channel nuts are specifically engineered to fit into the slots of channel tracks, providing a secure connection in applications where it is important to prevent loosening due to vibration or other forces. The self-locking feature in channel nuts is achieved through their design, which allows them to grip the bolt securely and resist movement.

In various mechanical applications, having a nut that locks itself in place can be crucial for safety and stability. This characteristic makes channel nuts particularly valuable in structures where maintenance may not be frequent and the integrity of the fastener connection must be maintained over time.

Other types of nuts, such as castle nuts, plain hex nuts, and internal-wrenching nuts, serve different purposes and don't have the specific design suited for drilled holes associated with channel systems, which accounts for their exclusion in this context.