Fasteners and Thread Types

Study Notes

Purpose of Fasteners

Screw threads hold parts together using bolts or screws.
Adjust parts relative to each other, as seen with adjusting screws in drafting tools.
Apply pressure to secure objects in place using setscrews.

Types of Threads

Helix: Spiral grooves on cylindrical surfaces.
External Threads: Located on bolts, cap screws, and wood screws.
Internal Threads: Found on nuts or tapped inside components.

Thread Measurements

Major Diameter: Largest diameter measured from crest to crest.
Minor Diameter: Smallest diameter of a thread.
Crest: Shallowest part of the thread.
Root: Deepest part of the thread.
Pitch: Distance between corresponding points on adjacent threads, typically in threads per inch.
Lead: Distance a thread travels with one complete revolution.

Thread Configurations

Single Threads: Lead equals pitch.
Multiple Threads: Lead exceeds one pitch, allowing quicker advancement (e.g., double threads move twice as far).

Fit Classes

Class 1: Loose fit for rough work.
Class 2: Free fit for general purposes.
Class 3: Medium fit for higher quality applications, like automotive use.
Class 4: Close fit for tight applications, as in aircraft engines.

Thread Characteristics

Thread Depth: Measurement from crest to root.
Thread Angle: Angle between the thread walls.
Standard Thread Angle: Typically 60 degrees.

Thread Direction

Right-Handed Threads: Advance clockwise; presumed if not specified.
Left-Handed Threads: Advance counterclockwise.

Tools for Threading

Tap: Tool for creating internal threads.
Small Threads: Often cut by hand.
Large Threads: Typically cut using a lathe.
Die: Tool for forming external threads.

Thread Standards

ANSI: American National Standard for Unified Threads.
Unified National Coarse (UNC): Most common thread series.
Unified National Fine (UNF): Stronger than UNC, providing secure fastening.
Unified National Extra Fine (UNEF): Highest tensile strength, suitable for high vibration applications.
Metric Thread: International standard based on ISO.

Specialized Threads

Square Thread: Transmits motion or power, challenging to manufacture due to perpendicular sides.
ACME Thread: Easier to manufacture with a 60-degree angle, used for rapid screw actions.
Sharp-V Thread: Provides friction holding; commonly used in brass components.
Knuckle Thread: Common on products like light bulbs and screw-type bottle tops.

Description

Explore the purpose and types of fasteners in this comprehensive quiz. Learn about different thread measurements, configurations, and how they function in various applications. Perfect for students studying engineering or mechanical design.