1. Topics Introduction Terminology Thread Specifications Bolts and Screws
MECH 1200
Introduction
Terminology
Thread Specifications
Bolts and Screws
Nuts and Locking Devices
Exercise Questions
Note: Refer to Chapter 6 in the text.

2. Introduction There are two thread standards:
MECH 1200
There are two thread standards:
The Unified Screw Thread Standard: Used in the U.S. It is based on a 60o thread angle.
Unified National Coarse (UNC) series: this is the most common series. Bolts, screws, and nuts of this series are used for general applications in which a quick assembly is required.
Unified National Fine (UNF) series: threads of this series are used for handling high tensile stresses, or when the length of engagement is limited such as screws in thin walls.
Unified National Special (UNS) series
The International Screw Thread Standard: most common standard, based also on the 60o thread angle.

3. Terminology
MECH 1200
Thread angle: the angle included between the sides of the thread, The ISO thread angle is 60 degrees.
Pitch: the distance between one point on a thread to the corresponding point on the next thread.
Number of threads per inch
Minor (root) diameter
Major (Outside) diameter
Lead: the distance a screw
thread advances in one revolution.
Thread Fit: How tight is the thread
engagement. Three classes of fit are used in the
unified system, loose, medium, and tight fits.
A for external and B for internal fits. (see p. 110)
Source: Siemens Technik Akademie Berlin

4. Thread Specifications
MECH 1200
Unified system threads:
Example: ¼ - 20 UNC-BX1 indicates a thread with an outer diameter is ¼ inch, with 20 threads per inch, the type of thread is UNC, and a B (internal) fit and a thread length of 1 inch.
Metric system threads:
Example: M10 ×1.5-6g indicates a Metric thread with an outside diameter of 10 mm and a pitch of 1.5 mm, the fit of the thread is 6g.
Bolts and Screws: The two words are used interchangeably, but generally, bolt is used when a nut is required to be used.
The shank of a bolt has a diameter that is equal to the major diameter.
Source: Siemens Technik Akademie Berlin

5. Common Bolts and Screws
MECH 1200
Carriage Bolt
used to fasten metal to wood. It has a square body right under the head to keep the wood from turning.
Machine Screw
used for vehicle body and metal sheets
Sheet Metal Screw
Set Screw
usually has no head, used to lock pulleys or gears to shafts
Socket Head Screw
has the strongest head style

6. Has a reduced shank, used for applications in which shock loads occur.
MECH 1200
Stud (Standing) Bolt
has threads on both ends, screwed permanently in one end and a nut on the other end.
Hexagon Through Bolt
Hexagon Fit Bolt
If the bolt goes through all parts and is fastened with a nut, then it is called a Through Bolt. When used to fix a part in position against movement it is called a Fit Bolt.
Anti-Fatigue Bolt
Has a reduced shank, used for applications in which shock loads occur.
Source of images in this slide: Siemens Technik Akademie Berlin

7. Nuts
MECH 1200
Hex nuts: Have a hexagonal shape, and has different grades
Castle Nut: Named so because it looks like a castle, used in applications where heavy vibrations occur, such as on wheels. Can handle light torques.only.
Wing nuts
Cap (Acorn) Nut

8. Fastener Locking Devices
MECH 1200
Screw locking devices are used to keep the nut from getting loose.
They can be friction based or non-friction based:
Friction based Locking devices
Internal tooth lock washer
External tooth lock washer
Spring lock washer
Lock washer
Safety wires
Non-Friction based Locking devices
Split pins
Nut lock plate
Tab washer

9. Exercise Questions What are the two thread standards?
MECH 1200
What are the two thread standards?
The Unified Screw Thread System and the ISO metric thread standard.
Thoroughly describe the bolt given by: ¼ - 28 UNF 2A
The bolt has an outer diameter of ¼ inch and a fine thread of 28 threads per inch (Unified National Fine thread series) and has a medium fit with external thread.
Thoroughly describe the thread bolt given by:
M10 x 1.25
The bolt is metric and its outer diameter is 10 mm and has a pitch of 1.25 mm

10. If a thread has 40 threads per inch what is its pitch?
MECH 1200
If a thread has 40 threads per inch what is its pitch?
Pitch = 1 inch / 40 = 0.025
Is each of the screw locking devices below friction based or not?
Yes No
Yes No No

11. What is the component shown in the figure below?
MECH 1200
What is the component shown in the figure below?
Castle Nut: used in applications that require low amount of torque, and where vibrations are common.