Capabilities of milling cutters: Which set best represents what can be performed on a milling machine using appropriate cutters and setups?

Introduction / Context:
Milling machines are versatile. With the correct cutters, arbors, and indexing/gear trains or CNC interpolation, they can produce a wide range of features beyond simple slots and faces.

Given Data / Assumptions:

• Availability of standard and form cutters (end mills, side-and-face, woodruff, involute gear cutters).
• Thread milling possible using single-form cutters or multi-tooth thread mills with synchronized motion.
• Dividing head (indexing) or CNC control for gear cutting and helical threads.

Concept / Approach:
Keyways are cut with end mills or woodruff cutters; external threads can be milled helically; spur gears are cut with involute gear cutters using indexing. The same platform supports complex profiles by coordinated toolpaths.

Step-by-Step Solution:

Verification / Alternative check:
Finished parts are checked using keyway gauges, thread plug/ring gauges, and gear tooth verniers or span measurements confirming feasibility on milling machines.

Why Other Options Are Wrong:
Each single-operation choice understates milling capability; claiming none is incorrect because all listed operations are routine with proper setup.

Common Pitfalls:
Poor fixturing or ignoring indexing accuracy during gear cutting; neglecting cutter selection per module or pitch.

Final Answer:
All of these (keyways, external threads by thread milling, and spur gear teeth)