Preventing rotation on shafts — attachment features Which combination is commonly used to attach parts to a cylindrical shaft so they do not rotate relative to it?

Introduction / Context:
Rotary power transmission often requires positive mechanical engagement between a shaft and a hub (gear, pulley, or coupling). Designers choose features that prevent slip under torque while enabling assembly, disassembly, and alignment.

Given Data / Assumptions:

• The part must not turn on the shaft.
• Standard machine elements are considered.
• Terminology: keyway (groove in hub), keyseat (groove in shaft), key (inserted element).

Concept / Approach:
A key transmits torque by bearing shear and compressive forces between the shaft keyseat and hub keyway. This positive drive is common, standardized, and easy to service. Alternatives include splines for higher torque or precision timing applications and interference fits plus set screws for light duty. Knurls increase friction, not positive drive. Bearings support rotation; they do not lock components to the shaft.

Step-by-Step Solution:

Verification / Alternative check:
Review machine design texts: keys and keyways are fundamental for torque transmission with standardized sizes (for example, Woodruff, square, or rectangular keys) per standards like ISO or ANSI.

Why Other Options Are Wrong:

• Lugs and bearings: lugs are attachment bosses; bearings permit rotation, not prevent it.
• Keyseats and bearings: bears same flaw—bearings allow rotation.
• Knurls and keys: knurling alone does not provide positive drive; the essential pair is key with keyway/keyseat.

Common Pitfalls:

• Failing to specify fit, length, and material for the key, leading to fretting or failure.
• Relying only on set screws for high-torque applications.

Final Answer:
Keys and keyways/keyseats