Introduction:
A milling machine is a versatile machine tool used to remove material from a workpiece using rotary cutters. The milling cutter is a crucial component of the milling machine as it performs the actual cutting operation. It is essential to mount the milling cutter securely to ensure accurate and efficient machining.

Explanation:
The correct answer to the question is option 'D' - Arbor. Let's understand why.

What is an arbor?
An arbor is a cylindrical shaft or spindle that is used to hold the milling cutter securely in place on a milling machine. It is usually made of hardened steel and is designed to provide stability and rigidity during the cutting process.

Function of an arbor:
The arbor serves several functions in the milling process:

1. Mounting the milling cutter: The primary function of the arbor is to hold the milling cutter securely. The cutter is mounted on the arbor using a keyway and key, ensuring a proper fit and preventing any slippage during operation.

2. Transmitting power: The arbor is responsible for transmitting power from the machine's spindle to the milling cutter. As the spindle rotates, the arbor transfers the rotational motion to the cutter, enabling it to perform the cutting operation.

3. Providing stability: The arbor's design and construction provide stability and rigidity to the milling cutter. This stability is crucial for achieving accurate and precise cuts, especially when machining complex or intricate workpieces.

4. Aligning the cutter: The arbor ensures proper alignment of the milling cutter with respect to the workpiece. It helps maintain the desired cutting angles and ensures that the cutter follows the intended path during the machining process.

Other components:
While the arbor holds the milling cutter, there are other components involved in mounting the cutter on a milling machine:

1. Drawbar: The drawbar is used to secure the arbor in the spindle of the milling machine. It applies force to tighten the connection between the arbor and the machine's spindle, ensuring a rigid and reliable setup.

2. Arbor support: The arbor support is a bracket-like structure that provides additional support to the arbor. It helps reduce vibration and deflection during the cutting process, further enhancing the stability and accuracy of the milling operation.

Conclusion:
In conclusion, a milling cutter is mounted on the arbor, which is a cylindrical shaft or spindle. The arbor plays a critical role in holding the cutter securely, transmitting power, providing stability, and aligning the cutter during the milling process. It is an essential part of a milling machine setup to ensure accurate and efficient machining.