2. Chapter 3
Fasteners

3. Objectives Identify types of threaded fasteners.
Identify the parts of a bolt.
Identify a bolt by diameter, threads per inch, length.
Identify types of bolts.
Identify nuts.

4. Objectives (Cont.) Identify locking nuts. Identify types of screws.
Identify types of washers.
Identify various nonthreaded fasteners.

5. Fasteners Simple devices that hold parts together or in place
Fasteners connect
Metal to metal
Plastic to metal
Plastic to plastic

6. Types of Fasteners Threaded fasteners Mechanical fasteners
Use screw threads to tighten two components together
Mechanical fasteners
Use mechanical force or process to hold parts together or make connection with component
Retainers limit component’s movement while allowing it to slide, pivot, or rotate

7. Threaded Fasteners Thread Typical rotation
Inclined plane wrapped in helix around central axis
Converts rotational movement to linear
Typical rotation
Clockwise rotation tightens fastener
Counterclockwise rotation loosens fastener

8. Linear Movement and Rotation

9. Special Applications Some applications require reverse threads
Left-hand threads
Slope downhill left to right
Opposite incline to right-hand threads
Tighten by counterclockwise rotation
Loosen by clockwise rotation

10. External Threads Formed on outside of fastener
Allow fastener to be screwed into threaded hole or nut

11. Internal Threads
Formed inside of hole
All nuts have internal threads

12. Bolts Externally threaded fasteners
Pass through holes in two or more parts
Parts are joined when nut is tightened onto bolt
Most bolts must be held to tighten nut
Consist of threads and shank

13. Screws Externally threaded fasteners
Pass through hole in one part
Thread into internally threaded hole (or form their own threads) in second part
Tightened or released by rotating head

14. Bolts vs. Screws Screws Bolts
Fasteners with thread diameters of less than 1/8″
Bolts
Fasteners with thread diameters larger than 1/8″

15. Machine Screws Thread into another component
Standard coarse and fine thread
Can be used with nuts
Both made in standard sizes
Conform to each other

16. Non-Machine Screws
Threads on screw cut matching threads in material into which it is tightened
Used on plastic or soft metal
Coarse threads on fasteners provide holding power

17. Tapping (Cutting Threads)
Process of cutting threads in hole
Tap tool (tap) is used to cut internal threads

18. Bolts and Machine Screws
Head and body
Body is divided into threaded portion and shank
No shank if threads go completely to head

19. Bearing Surface Area underneath head Cap screw (round bearing surface)
Usually flat and smooth to reduce friction
Applies clamping force to components being tightened
Cap screw (round bearing surface)
Flat head fastener (tapered bearing surface)

20. Bolt and Screw Designations
Designated by one or more
Thread form nomenclature
Type of head
Type of head drive system
Special features

21. Thread Form Nomenclature
Identifies fasteners by
Diameter
Threads per inch
Length
Conforms to either
US customary thread form system
Metric thread form system

22. Thread Standards
Terms to identify conforming threads—Unified National threads, inch threads, English threads
Conforming thread standards are set by
ASME
ANSI
IOS
Standards set for fastener diameter and threads per inch

23. Bolt and Machine Screw Identification
US customary bolts and machine screws are identified by
Diameter
Threads per inch (tpi)
Length
Format
Diameterthreads per inch × length

24. Metric Bolts Identified by Diameter (in millimeters) Pitch
Distance from tip of one thread to tip of next
Amount of linear distance that fastener moves in one revolution

25. Metric Bolt Identification Format
Format (in this order on head)
Capital M
Bolt body diameter in millimeters
Dash (spoken as “by”)
Thread pitch
Example: M8–1.25

26. Metric Bolt Identification
Standardized diameters and thread pitches
Identified by pitch
Smaller number after dash means more threads per bolt
If no pitch, default is coarse thread pitch
Multiplication symbol and following number indicates bolt length

27. Bolt and Screw Identification
Type of head, drive system, or combination
Head shape determines type of head
Hexagonal (hex)-shaped
Square
Pan-shaped
Flat

28. Hexagonal Head Fasteners (Flats)
Can be held or rotated using standard wrenches because of standardized head dimensions
Distance across two opposite sides of head conforms to standard size established for bolt thread diameters

29. Hex Flange (Washer) Head Fasteners
Washer integrated with head
Increases bearing surface
Distributes torque load over larger surface area than standard hex head

30. Serrated (Binding) Head Bolts
Raised serrations on bearing surface lock into surface of component
Prevents bolt from loosening or backing out
Angled serrations keep vibrations from loosening bolt

31. Square Head Fasteners Four-sided head fits into square opening
Not necessary to hold head with wrench while tightening nut
Exposed threaded end used as stud

32. Types of Screw Heads

33. Drive Systems
Hexagon socket head
Hex head, socket head

34. Drive Systems (Cont.) Torx-type (hexalobular)
Size designated by “T” followed by number
External (reverse) Torx fastener
Size designated by “E”

35. Drive Systems (Cont.)
Cross-recessed drive
Phillips-type
JIS

36. Drive Systems (Cont.)
Combination drive systems

37. Special Feature Fasteners
Threaded fastener with unique design
Intended to be used for specific applications

38. Stud Usually threaded at both ends Different thread type on each end
One end installed in part
Other end accepts nut
Different thread type on each end

39. Stud Bolt Head is anchored in part
Threaded end protrudes to act as stud

40. Square Shoulder (Carriage) Bolt
Shoulder located directly under head
Inserted into preformed hole in one component so nut can be applied to threaded end to attach second component

41. Hex Socket Head Shoulder Screw
Hex socket recess in head
Round shoulder shank diameter is larger than fastener thread diameter

42. SEMS Fastener Washer is permanently attached to screw, bolt, or nut
Fastener and washer are installed in one step

43. Set Screw
Threaded fastener used to mechanically hold two components in position with each other
Usually does not have head
Intended to be installed flush with or below surface

44. Self-Threading (Thread Forming) Screw
Special threads and ends displace and reshape material, forming internal threads
Normally used in soft metals and plastics
Can be used to produce machine threads or screw threads
Internal threads formed during installation are permanent

45. Self-Threading (Thread Forming) Screw (Cont.)
When screw is reinstalled, threads must screw into original internal threads
To align screw with original threads
Rotate screw backward by hand until it clicks
Rotate screw clockwise to tighten

46. Sheet Metal Screw Fastens thin metal sheets or light-duty plastics
Self-threading
Internal threads remain after screw installed

47. Thumb Screw Screw with special designed heads
Tightened and loosened by hand

48. Nut
Internally threaded fastener that screws onto externally threaded fasteners
Applies holding torque to keep components together under normal vibration
Bolts pass through two components and use a nut to keep parts together

49. Typical Nuts
Hex nuts
Square nuts
Locknuts
Finger-tightened nuts

50. Hex Nut
Six-sided nut that screws onto bolts
Identified by thread form

51. Flange Hex (Hex Washer Head) Nut
Washer bearing surface on one side of nut
Distributes tightening force over larger surface area
Nut can be torqued to higher value

52. Locknut
Nut deformation or insert keeps nut from spinning freely and backing off

53. Wingnut
Designed to be installed and tightened by hand

54. Washers Flat washer Thin disc with hole in middle Used between
Surface of components and nut
Surface of components and fastener head
Allows large clamping force without damage

55. Washers (Cont.) Lock washer Keeps fasteners from loosening
Can be used to improve electrical connections

56. Thread Adhesive
Applied to fastener threads to prevent loosening due to vibration
When fastener is reinstalled
Remove old adhesive
Reapply fresh adhesive with same holding power
Color indicates qualities (strength, heat resistance, penetrating ability)

57. Adhesive Fasteners
Threaded fastener with correct amount of adhesive preapplied
When fastener is installed, friction from tightening releases adhesive
Also called microencapsulated fasteners

58. Removing Cured Adhesive
Dried adhesive must be removed from threaded hole
Determine
Fastener thread form and diameter
Thread pitch
Select tap with same thread type
Thread tap into hole to remove old adhesive

59. Thread Repair Restoring threaded hole to its original thread form
Metal threaded insert may sometimes be installed
To repair threaded holes, follow manufacturer’s repair procedure

60. Torque System
Torque
Twisting force that tries to rotate fastener
Stress keeps fastener tight (torqued)
If torqued too much, fastener could break or components could be damaged
If torqued too little, fastener could loosen during operation

61. Correct Torque Torque must be enough to
Stretch fastener without breaking it
Hold components together without damage
Torque must not exceed strength of fastener
Correct process must be used

62. Need for Torque
Vibrations from engine add stress parallel to center of fastener
Screw tends to back out of threads
Nut tends to unscrew from bolt

63. Thermal Expansion
Components expand when engine heats up and contract when engine cools off, causing fasteners to loosen
Thermal expansion and contraction varies in different parts of engine
Same fastener used in two locations may require two different torque values
Follow manufacturer’s torque requirements

64. Engineered Stretch
Fasteners are able to stretch and remain under tension
Fasteners return to original shape when loosened
Amount of stretch is engineered to adequately hold each piece of equipment in place
Strength of fastener affects amount of torque applied

65. Torque Specification Torque specification must account for
Elastic limit
Tensile strength
Torque value cannot be greater than elastic limit

66. Sustaining Torque
Ability of threaded fastener to sustain torque through threads depends on
Diameter of fastener
Number and type of threads
Grade of material
Tensile strength is determined by
Minor diameter of fastener
Fastener material

67. Fastener Grade Indicates metal alloy composition of fastener
Composition contributes to elastic limit and tensile strength
Higher grade bolt has greater strength but lower elasticity than lower grade bolt

68. Torque Wrench
Torque applied to fastener—a force acting at a distance from the center of the fastener
Torque is applied and measured with torque wrench
It is important to read and understand torque wrench instructions

69. Selecting Torque Wrench
Identify torque specification units for fastener
In-lb (inch-pounds)
Ft-lb (foot-pounds)
N·m (newton-meters)
Select wrench that
Can measure needed units
Includes torque range to be measured

70. Tightening in Proper Sequence
Follow equipment manufacturer’s torque sequence
Some fasteners can be torqued in one step
Others must be torqued in stages (especially for high torque values)
Install all fasteners before tightening any of them

71. Nonthreaded Fasteners
Connect two parts together to make one assembly
Use mechanical holding process other than threads
May have threads, but threading is not primary means of connection

72. Clamps Circular flat metal or wire bands
Apply pressure to one component to keep it fastened to another component
Types of clamps
Wire clamp
Spring clamp
Rigid clamp
Flexible hose clamp

73. Wire Clamp and Spring Clamp

74. Rigid Clamp and Flexible Hose Clamp

75. Spring Safety Hooks (Clasp)
Connect parts together loosely
Spring keeps it closed when attached
Can be quickly taken on and off by
Depressing spring
Hooking or unhooking clasp

76. Dowels and Sleeves Dowels (or dowel pins)
Solid metal fasteners used to perfectly align two parts
Usually slip into mating hole with just enough clearance to enter without friction or looseness
Dowel sleeves are similar to dowels, but hollow

77. Retainers Keep a component in place
Either lock onto something or lock in place inside something

78. Types of Retainers Push-on retainer E-clip retainer
Round press-on clip that holds two parts in place
When pushed onto shaft, spring-loaded tabs press into surface, locking retainer in place
E-clip retainer
Slides into grooves on outside of shaft and locks in place

79. Clips
Hairpin clip
R-clip

80. Snap Rings External Internal Fit into grooves to retain parts on shaft
Installed into grooves inside a bore

81. Circlips Circlips (hookless snap rings)
Assembled into an internal groove in a bore
Keep wrist pins in place

82. Roll Pins Spring steel rectangles rolled into cylinders
Driven in place; held in place by spring pressure
Used to lock parts in place

83. Cotter Pins Used to retain components on a shaft Split pin retainers
Inserted through hole in shaft
Ends are spread to keep pin from backing out