Threaded Fastener

INTRODUCTION

A threaded fastener is a discrete piece of hardware that has internal or external screw threads. They are usually used for the assembly of multiple parts and facilitate disassembly.

Types of Fastening

1. Permanent

1. Welding
2. Gluing
3. Riveting

 

2. Temporary

1. Threaded Fastener

1. Bolts: They are basically threaded fasteners normally used with nuts.
2. Studs: They are externally threaded headless fasteners. One end usually meets a tapped component and the other with a standard nut.
3. Screws: They engage either with preformed or self made internal threads.

2. Non-Threaded Fastener

1. Keys
2. Pin

There are different forms of bolt and screw heads for a different usage. These include bolt heads of square, hexagonal or eye shape and screw heads of hexagonal, Fillister, button head, counter sunk or Phillips type.

Application of Threads

1. To hold parts together.
2. To move part(s) relative to others.

Thread Terminology

• Right Hand Thread: Thread that will assemble when turned clockwise.
• Left Hand Thread: Thread that will assemble when turned anti clockwise.
• Crest: The peak edge of a thread.
• Root: The Bottom of the thread cut into a cylindrical body.
• Thread angle: The angle between threads faces.
• Pitch: The distance between crests of threads.
• Lead: The distance a screw will advance when turned 360°.
• Major Diameter: The largest diameter on an internal or external thread.
• Minor Diameter: The smallest diameter on an internal or external thread.
• Thread Form: It is profile shape of the thread.

Screw threads formed in this way have two functions to perform in general:

(a) To transmit power - Square. ACME, Buttress, Knuckle types of thread forms is useful for this purpose.

(b) To secure one member to another- V-threads are most useful for this purpose.

V-threads are generally used for securing because they do not shake loose due to the wedging action provided by the thread. Square threads give higher efficiency due to a low friction.