Step 1: Understand the function of different needle types in knitting. The primary goal is to form a new loop and cast off the old one. This requires the hook to be able to open to catch new yarn and close to secure the new loop while the old one is cast off.
Step 2: Analyze how each needle type closes its hook.
- Latch Needle: Has a pivoting latch that closes the hook automatically when the old loop slides up the needle shank. It is self-acting.
- Compound Needle: Consists of two parts, a hook element and a sliding tongue or closing element. The parts move relative to each other to open or close the hook. It is also self-contained.
- Bearded Needle: Has a flexible hook (the "beard") that is bent back into a groove on the needle shank to close it. This bending action is performed by an external element called a "presser bar." Therefore, it requires an external device.
- Sewing Needle: Used for sewing, not for loop formation in knitting machines.
Conclusion: The bearded needle requires an external presser bar to close its hook.