Differences between Tapping and Threading:

Workpieces

• Tapping: Used for making internal threads, like cutting threads inside a hole to fit screws or bolts.
• Threading: Can make both internal and external threads. External threading is usually done on cylindrical parts like bolts or rods.

Tools

• Tapping: Uses a tap (a cutting tool) to cut threads inside a pre-drilled hole. there is a cutting edge that cuts away material to form the threads.
• Threading: Uses dies or thread milling cutters for external threads, and taps for internal threads.

Process

• Tapping: Drill a hole first, which needs to be slightly larger than the diameter of the desired internal thread so that the tap can enter and cut the thread. Then use a tap to cut threads inside. The tap needs to be rotated and fed carefully to ensure thread accuracy.
• Threading: For external threads, a die is rotated around the workpiece to cut threads. Internal threading is similar to tapping.

Methods

• Tapping: Can be done manually or with CNC machines. Manual tapping requires skill, while CNC tapping is more precise and efficient.
• Threading: Common methods include manual threading, lathe threading, and CNC threading.

Applications

• Tapping: Used for parts that need internal threads, like nut holes or installation holes in machinery. Tapping is primarily used in holes in metal or other materials to prepare them so that bolts or screws can be screwed in.
• Threading: Used for parts that need both internal threads (such as in a nut or drilled hole) and external threads  (such as on a bolt or screw) .

Accuracy and Efficiency

• Tapping: Best for high-precision internal threads, especially small holes. CNC tapping is very accurate and efficient.
• Threading: External threading is usually faster, especially with thread rolling or CNC machining.

In summary, tapping is mainly for internal threads, while threading covers both internal and external threads. They have different tools, processes, and applications.