Fasteners and Thread Types

Questions and Answers

What is the purpose of screws?

To hold parts together

To apply pressure on an object

To adjust parts with respect to each other

All of the above (correct)

Define 'Helix'.

The spiral grooves cut into the surface of cylinders.

What are 'External' threads?

Threads found on a bolt, cap screw, wood screw, etc.

What are 'Internal' threads?

Threads found on a nut or tapped inside a part. Signup and view all the answers

What is 'Major Diameter'?

The largest diameter of a thread, measured from crest to crest. Signup and view all the answers

What is 'Minor Diameter'?

The smallest diameter of a thread. Signup and view all the answers

Define 'Pitch'.

The distance from one point on the thread to the corresponding point on the next form. Signup and view all the answers

What is 'Lead' in the context of threads?

The distance a thread moves in one revolution. Signup and view all the answers

What are the four standardized classes of fit?

Loose fit, Free fit, Medium fit, Close fit Signup and view all the answers

What degree is the angle created by the slope of a standard thread?

60 degrees Signup and view all the answers

What is a tap used for?

Forming small internal threads Signup and view all the answers

Which type of threads allows for rapid advancement of parts?

Multiple threads Signup and view all the answers

What is 'Class of Fit'?

Four standardized classes defining fit quality for threads. Signup and view all the answers

Match the following thread types with their characteristics:

Square Thread = Used to transmit motion or power along the axis of the screw ACME Thread = Modification of square thread with a 60 degree angle Sharp-V Thread = Fits tightly and is used where friction holding is important Knuckle Thread = Used for light bulbs and screw-type bottle tops Signup and view all the answers

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.