1. Automotive fasteners and measurements

2. The metric system
European and Asian [with the exception of Sweden and the UK] manufactures have built their automobiles to metric specifications since the invention of the automobile
In the mid 1970s the United States, Sweden and the UK began the switch to the metric system

3. The switch to metric
Beginning in 1977 when any new component was introduced on an American made vehicle where factory retooling was needed, the threads for all the fasteners were machined to metric specifications
Nearly all fasteners on modern domestic cars are metric but you may still find some standard threads on components that have not significantly changed in over 35 years [often on commercial trucks]

4. Metric is simpler
The metric system does not use fractional measurements
If your trying to find a wrench where a 13mm is too small and a 15mm is too big – the answer is simple – 14mm
Wrench sizes in the US Standard system are fractional
If your trying to find a wrench where a ½” is too small and a 5/8” is too big – the answer requires a good grasp of fractions and often requires you find the dreaded ‘lowest common denominator’

5. Meters
Meter Stick
Yard Stick
A meter is a little bit longer than a yard – inches to be exact

6. Meters 1 meter can be divided into:
10 decameters [rarely used]
100 centimeters {cm}
1000 millimeters {mm}
Millimeters are the most common unit used in automotive specifications but centimeters are occasional used
10 millimeters = 1 centimeter

7. Abbreviations
When working with dimensions that are smaller than the base unit lower case letters are used
Upper case letters are used in abbreviations of units larger than the base unit
5 mm represents 5 millimeters [5/1000 of a meter]
5 Mm represents 5 megameters [5 million meters]

8. Fractions are not used in metric dimensions
Fractions should never be used with metric dimensions
When you measure something with a metric ruler that is halfway between 23 and 24 cm you should record the dimension as 23.5 cm

9. Hex head bolt dimensions
There are four primary dimensions of a hex head bolt:
[A] Thread diameter
[B] Thread length
[C] Thread pitch
[D] Hex size [distance between flats]

10. Distance between flats
The hex size determines the size of the wrench needed to loosen and tighten the bolt
The hex size is not standardized
A bolt with a diameter of 8mm and a thread pitch of 1.25mm will have a hex size of 12mm on an Asian car
An 8mm bolt with a 1.25mm pitch will have a hex size of 13mm on a European car
8 x 1.25mm
12mm
Asian
8 x 1.25mm
13mm
European

11. Thread pitch
1.5mm
In the metric system the thread pitch is the distance in millimeters between each thread
Threads that are spacedd close together are called ‘fine’ whereas threads that are spaced far apart all called ‘coarse’
Coarse
1.25mm
Fine

12. Metric standard and fine thread pitch
Bolt Dia. Standard Fine Super Fine 6mm 1.0 7mm 1.0 8mm mm mm mm mm mm mm 2.5

13. US standard coarse and fine thread pitch
Bolt Dia. UNC Coarse UNF Fine 1/4” /16” /8” /16” /2” /16” /8” /4” 10 16

14. USS and SAE
In the US system coarse thread bolts may be called UNC or USS bolts [Unified National Coarse or United States Standard]
Fine thread bolts may be called UNF or SAE [Unified National Fine or Society of Automotive Engineers]

15. Coarse thread vs. fine thread
Fine thread bolts have superior holding ability but they can only be used with hard metals [steel]
Soft metals such as aluminum, cast iron and brass will not tolerate the stress that can be applied to a fine thread bolt

16. Determining thread diameter
Thread diameter is measured in the threaded end of the bolt between the high points of the threads [peak to peak]
The shank [unthreaded section is normally slightly smaller than the threaded section
Shank

17. Determining bolt length
Bolt length is the distance between the bottom of the bolt head and the end of the threads
Universal replacement bolts sold in auto supply stores normally come in 5mm increments
40mm

18. Determining thread pitch
Thread pitch is measured with a thread pitch gauge
Place the teeth of one of the gage blades lengthwise along the threads of the bolt
If all of the teeth fall into the thread valleys the thread pitch is equal to the number stamped on the blade

19. Internal thread pitch
The thread pitch gauge can also measure internal threads
It is not easy to see the gauge teeth when measuring internal threads
Identifying the correct pitch on an internal thread is done more by feel than by eye

20. Bolt dimensions
When ordering metric add the letter ‘M’ in front of the dimensions
The order of dimensions is:
Diameter
Pitch
Length
M8 x
The bolt listed here:
Is 8mm in diameter
Has a 1.25mm thread pitch
Is 40mm long

21. US standard bolts
US Standard bolts may have a UNC or UNF prefix [Unified National Coarse or Unified National Fine]
The bolt dimensions are in the same order [diameter, pitch and length]
1/4 x /4
Thread pitch is expressed in threads per inch in US Standard bolt nomenclature

22. Bolt gauge
Bolt distributers often give away plastic bolt gauges that make it easier to identify bolt diameter and length

23. Grade number
The bolts used to hold automotive parts together must be stronger than general purpose bolts used for household applications
Bolts are graded by the tensile strength of the steel the bold is made from
Tensile strength is the maximum amount of force [pull] that can be applied to a bolt before the bolt will not return to its original length after the pressure is released
The yield strength is the amount of force [pull] it takes to make the bolt break

24. US standard bolt grade numbers
Grade 3 – approx 100,000 psi / sq in
Should not be used for automotive applications
Grade 5 – 120,000 psi /sq in
OK for low stress automotive uses – accessory brackets, exhaust system etc.
Grade 8 – 150,00 psi / sq in
Needed for high stress components – rod bolts, clutch and flywheel bolts etc.

25. Metric bolt grade numbers
Metric bolts have a number stamped on the head of the bolt that indicates both tensile and yield strength
10.9
The number in front of the decimal point is 1/10th of the tensile strength measured in kg/mm2
In the example here the bolt is made from steel that can withstand 100 kilograms of force over one square millimeter and still return to its original length
The number after the decimal point is the 1/10th of the percentage of tensile strength to the yield strength
In the example the tensile strength is 90% of the yield strength

26. Metric grade numbers Unmarked - equivalent of Grade 3
Should not be used for automotive applications
8.8 Equivalent to Grade 5
OK for low stress automotive uses – accessory brackets, exhaust system etc.
10.9 Equivalent to Grade 8
Needed for high stress components – rod bolts, clutch and flywheel bolts etc.

27. Flat washers
A flat washer is placed between the head of the bolt and the component for a number of reasons:
The flat washer distributes the clamping load over a greater surface area
The use of flat washers helps to achieve a more accurate torque value
The flat washer prevents gouging on soft metal or painted/plated surfaces
Never use more than one flat washer per bolt
Besides the fact that the retaining bolt will loosen over time the use of multiple washers is evidence of shoddy workmanship

28. Lock washers
Split lock washers are made of spring steel and have a sharp edge that bites into the base metal to prevent the bolt from loosening
Split lock washers are not very effective and are not normally found on modern cars
Star washers have sharp radial spurs that dig into the base metal to prevent loosening
Star washers are often used on chassis ground electrical terminals
Wave washers and Belleville washers are made of thin spring steel and provide a small amount of spring tension to the clamping load
Split
Star
Wave

29. Serrated lower surface
Flange bolts
Most modern automotive threaded fasteners usually have the flat washer integrated into the head of the bolt or nut.
Often the lower surface of the integrated washer is serrated to help prevent the nut or bolt from loosening
The integrated washer allows the hex to be smaller – which allows the bolt to fit into tight places making installation easier
This type of bolt is called a ‘Flange Bolt’
Serrated lower surface

30. Nylock nuts
Nylock nuts are often used in applications where minimal clamping force is needed – valve covers etc.
Nylock nuts have a nylon ring embedded in a groove at the top of the nut that prevents the nut loosening
Nylon ring
Nylock nuts cannot be used in high temperature applications

31. Top thread is out of round
All metal lock nuts
This type of nut is similar in appearance to a nylock nut but can withstand high temperatures
Instead of nylon the top thread is pinched inward at four points and is slightly out of round
Top thread is out of round

32. Allen and Torx head bolts
Allen head and Torx head bolts have recessed caps that require an Allen or Torx sockets
Torx head bolts have become popular in recent years because they provide the maximum amount of surface area exposed to torquing force of any common fastener so they are less likely to be deformed during torquing and de-torquing
The Torx head bolt allows for more accurate torquing of machine assembled components
Allen head
Torx head

33. Torx head screws and bolts
Torx head screws are commonly used in the assembly of small lightweight chassis components
Headlight assemblies
Instrument clusters
Heating and air conditioning under-dash components etc.
The size of a female Torx screw is expressed as a number after the letter ‘T’
Torx screws normally range from T8 to T65

34. External Torx bolt heads
External [male] Torx head screws are commonly found in modern automotive engines
External Torx head bolts will require special sockets that have the letter ‘E’ preceding the size number
External Torx head screws and bolts normally range from E4 to E24
The numbers for external Torx bolts are much smaller than internal
A T55 bolt has the same internal dimensions as the external dimensions of an E12 bolt

35. Machine screws
Machine screws are small screws used in subassemblies such as instrument clusters, heater controls etc.
US Standard machine screws are numbered
When as hash mark ‘#’ is placed in front of a number it denotes a US Standard machine screw
Metric machine screws are preceded by the letter M and do not use the hash mark ‘#’ so the size designation is the same as regular metric bolts
Unlike conventional bolts, machine screws are normally threaded their full length

36. US Standard machine screws
num pitch dia. # ” # ” # #10 24 & #

37. Metric machine screws
num pitch dia. M mm M mm M mm M mm M mm M mm M mm M mm M mm M mm

38. Thread engagement
Bolts that are threaded into engine blocks, cylinder heads, etc. must be long enough to insure the threads on the bolt have sufficient grip to withstand the stress when the bolt is torqued to specifications.

39. Bolt to Short
If the bolt is too short the threads in the block or the bolt will be stripped
If the threads in the block are stripped the hole will need to be drilled oversize and a thread insert [Heli-Coil] installed

40. Bolt to Long
If the bolt is too long it will bottom out and bind in the hold.
Do not install extra washers to correct this –additional washers will reduce the clamping force
If the bolt snaps when its torqued you will not be able to remove the broken stub with an EZ-out because the threads are bound

41. Thread engagement – Dia./Length ratio
Lightly stressed bolts that thread into cast iron or steel housings should have a minimum threat engagement ratio of 1 to 1
A 1.5 ratio is better
Aluminum, brass and other soft metals require more thread engagement – typically 2 to 3 times the bolt diameter
8 mm
8 mm

42. Thread engagement – visual check
8 mm
When installing a bolt check how far the head of the bolt is from the component when the threads first catch.
The head of the bolt should extend 1 to 1.5 times its diameter on lightly stressed bolts
Heavily stressed bolts [head bolts, main bearing cap bolts etc.] will have threads engaged 3 to 4 times their diameter
8 mm

43. Shoulder bolts
Shoulder bolts have a shank that is much wider than the threads
They allow for a fixed gap between the housing/flange surface and the head of the bolt
Shoulder bolts are found on flexible exhaust flanges and valve covers where soft silicone gaskets are used
The shoulder bolt prevents the soft rubber gasket from being damaged by over tightening the bolts

44. Left hand threaded fasteners
Nearly all threaded fasteners use right hand threads
A right hand threaded bolt is tightened when rotated clockwise – to the right as viewed at the top
Left hand thread fasteners a threaded in the opposite direction
A left hand threaded bolt is tightened when turned counter-clockwise – to the left as viewed at the top
Left handed fasteners are often stamped with the letter ‘L’

45. Applications for left hand threads
The most common application for left handed threads are the tie rod ends in the steering linkage
Right hand threads
Sleeve
Left hand threads
The outboard tie rod shaft has right hand threads and a right hand locknut
The inboard tie rod shaft has left hand threads and a left hand lock nut
The center sleeve has left hand threads on the inboard end and right hand threads on the outboard end.
When the sleeve is rotated in one direction – the tie rod gets longer. Rotate the sleeve in the opposite direction and the tie rod gets shorter

46. Studs
Intake and exhaust are often retained by studs and nuts instead of bolts
Studs are often used on aluminum heads and blocks.
They eliminate the potential for damage to the soft threads in the aluminum castings when components are removed and installed

47. Studs
An unthreaded ‘shoulder’ separates the two threaded ends of the stud
The shoulder is slightly larger than the threaded sections. This allows the stud to be retained tightly to the casting
Most studs for modern engines have a external [male] Torx end that simplifies installation
Torx head
Shoulder

48. Hand Wrenches Adjustable Open end Box end Combination Flare nut
Ratcheting

49. Adjustable wrench
Only two stress point
Adjustable wrenches should never be used to loosen or tighten automotive fasteners
They often found in an emergency tool kit but you’d be better off with an inexpensive set of sockets
There are many different types, but all of them will damaged the head of the bolt if a large amount of torque is applied

50. Open end wrench
Only useful in places where a socket or box end wrench can’t reach – exhaust manifold bolts, valve lash adjuster lock nuts etc.
The wrench size of each end of a double open end wrench is a different – 6 wrenches can cover 12 sizes

51. Open end
Only two stress points
Like the adjustable wrench the open end wrench only applies pressure on two corners of the bolt head
Never apply a large amount of torque to the head of a bolt with an open end wrench unless there is no other alternative
Once the bolt has been loosened it is often used to work the bolt out of the threads as it is much faster to reposition than a box end wrench

52. Box end wrenches Two general types of box end wrenches
6 point
12 point
The advantage of a box end wrench is that when the bolt is torqued/de-torqued pressure is applied equally to all six flats

53. Red indicates high stress area
Box end wrenches
Pressure is applied equally at six points on the bolt head
The design of the box end allows pressure to be applied away from the corners
This makes it less prone to round the corners of the bolt head when high torque is applied
Red indicates high stress area

54. Box end wrenches
The 6 point box end wrench has twice the surface area in contact with the bolt head so it is less likely to round off the corners on the head of the bolt
The 12 point box end wrench is easier to work with as it only needs to be rotated 30 degrees to engage another set of flats

55. Box end wrenches
The 6 point box end wrench applies pressure over a surface area that is twice as large as that of a 12 point box end wrench
The pressure is applied away from the corners where the metal is thin
The six point open end wrench and the 6 point socket can apply more torque to a bolt head then any other type of wrench or socket without rounding off the corners

56. Offset box end wrenches
Like the double open end wrench the double box wrench has two different sizes
Most double box wrenches are slightly offset – typically about ½”
Deep offset box wrenches have an offset of 1 to 1 ½” and are designed to get around obstacles.
Deep offset box wrenches are often needed to remove carburetors and distributers and are often used in valve adjustment on commercial diesel engines

57. Flare nut wrench
Flare nut wrenches are used to loosen and tighten the nuts on steel brake and hydraulic lines
The are open at one end so that they can slip over the steel brake line
Unlike conventional open end wrenches they make contact with the nut at 5 points
They are also thicker than conventional wrenches

58. Specialty wrenches
Specialty wrenches are wrenches that are bent or curved to service one component on one brand of vehicle
New car dealers will have hundreds of specialty tools in their tool room
Some specialty tools are available from tool manufactures
Often mechanics make their own specialty tools by heating and bending an ordinary wrench into a shape that will fit

59. Socket Wrenches
Socket wrenches are the best type of wrench to remove and install automotive components
Like a box end wrench they provide maximum amount surface area for the forces of torqueing and de-torqueing the bolt without damaging the flats on the bolt head
Unlike hand wrenches sockets can be attached to a torque wrench so that a measured amount of torque is applied

60. Thin wall and Impact sockets
Weak spot
There are two general types of sockets:
Thin wall
Impact
Thin wall sockets are designed for hand tightening
They are thinner than impact sockets so they can fit into places that an impact socket cannot

61. Thin wall and Impact sockets
Thin wall sockets should never be used with an impact wrench
Serious injury can result when the socket shatters and the pieces fly outward at high speed
Thin wall sockets are normally chrome plated but an industrial black anodized finish is also available

62. Impact sockets
Thicker wall
Impact sockets have a thicker wall which makes them much stronger than thin wall sockets
Impact sockets normally have a dull black oxide finish
Black oxide is a type of rust. It forms a bond with the steel that prevents further rusting
Impact sockets have a hole drilled through the base of the socket so that the socket can be secured to an impact extension
A spring loaded pin holds the socket secured to the extension so that it cannot fly off at high speeds
Hole for retaining pin

63. Shallow and deep sockets
Shallow sockets are designed to fit bolt heads and nuts where there are only a few exposed bolt threads
Deep sockets are intended for nuts where there are too many exposed bolt threads to allow the use of a shallow socket
Always use a shallow socket when ever possible
A shallow socket transmits more torque and helps keep the torqueing force centered on the bolt

64. Broach depth Deep sockets can have a variety of broach depths
In a deep broach socket the hex is machined very far down the center of the socket
When installing fasteners the deep broach allows the bolt or nut to drop to the bottom of the socket
Most deep sockets are shallow broached – the nuts are held close to the open end of the socket where they can easily engage stud threads

65. Spark plug socket
13/16” hex
Special deep broached sockets are made for the removal and installation of spark plugs
Spark plug sockets have a recessed area where a soft rubber sleeve is installed
The rubber sleeve grabs a hold of the spark plug to prevent it falling out of the socket
The rubber sleeve also protects the glass insulator from being damaged during installation
Rubber sleeve

66. Removing and installing studs
Studs that a relatively new and show very little evidence of corrosion can sometimes be removed using an ‘E’ type [external] Torx socket
If the socket does not fit tightly onto the Torx end of the stud use the double nut method or apply heat to the casting around the stud

67. Double nutting
The double nutting technique for stud removal should be used when there is no Torx end on the stud or the Torx end is too corroded to use an ‘E’ type Torx socket
Corroded Torx end

68. Double nutting
Thread two nuts onto the stud

69. Double nutting
Hold the lower nut with a wrench while tightening the upper nut

70. Double nutting
To gain extra grip arrange the wrenches so they can be squeezed like a pair of pliers

71. Double nutting
Loosen the stud by turning the lower nut with a box end wrench

72. Double nutting
Continue turning until stud is free from casting

73. Double nutting
To remove the nuts from the stud hold one nut with a wrench while turning the other nut counter-clockwise

74. Stud remover A stud remover tool damages the threads
It should only be used if the stud is going to be replaced
The stud remover can also be used to remove broken bolts if there is at least ¾” of bolt exposed
The tool connects to a ½” ratchet and extension

75. Using heat to remove rusted studs
Heat is essential to the process of removing corroded studs and bolts
An oxy-acetylene torch is needed to provide the level of heat needed to loosen rusted bolts
Heat causes the casting to expand – opening up the threaded hole so that the stud or bolt can be turned easily

76. Using heat to remove rusted studs
A rosette or cutting tip is needed to produce the kind of heat necessary to loosen the stud
The tip of the torch is moved back and forth over the casting immediately surrounding the stud
The flame is not directed onto the stud – we want the stud to remain cooler than the casting

77. Install the stud remover
Working as fast as possible install the stud remover using a long ½” drive extension

78. Install the stud remover
More heat may be needed if the threads begin to bind as the stud is worked out of the threads

79. Clean up the threads
The threads in the casting should be cleaned of any debris using a tap
This homemade 8 x 1.25 mm thread chaser was made from an old ¼” socket and a tap

80. Tap and Die
The size and thread pitch of the tap is printed or stamped on the side of the tap

81. Removing broken bolts
When studs or bolts are broken with little or no exposed threads the only way to remove them requires drilling

82. Center punch
A center punch is used to make a dimple in the center of the broken bolt
The dimple prevents the drill bit from ‘walking’ when the drill is first started
The dimple must be a close to the center of the broken bolt as possible

83. Make a dimple
Locate the point as close to the center of the broken bolt as possible then strike the center punch with a hammer

84. Drill a pilot hole Start with a small drill bit
Make sure that you hold the drill as close as possible to the bolt hole center axis

85. Drill a pilot hole
If the hole is not blind drill the pilot hole all the way through
If the hole is blind, check the depth often to make sure that you don’t drill all the way through the manifold or cylinder head

86. Enlarge the hole
Install a slightly larger drill bit and drill through the pilot hole
Keep enlarging the hole until the hole is big enough to accept an EZ-out

87. EZ-Outs EZ-Outs are a brand of screw extractors
They utilize a tapered, spiral hardened steel screw that wedges itself tighter as torque is applied in a counter-clockwise direction [loosening]

88. Recommended drill size
5/32”
Printed on the side of the EZ-Out is the recommended drill bit size to enlarge the hole to

89. Drill Index The case that holds drill bits is called a ‘drill index’
The drill size can be determined by the smallest hole in the drill index that the drill bit will fit

90. Hammer in the EZ-Out
Tap the EZ-Out with a hammer until the flutes are firmly engaged in the drill hole

91. Install a tap handle to turn the EZ-Out
The EZ-Out can be turned using a tap handle

92. Using a 4 point socket to turn the EZ-Out
In tight spaces a 4 or 8 point socket can be used in conjunction with a ratchet and extension to rotate the EZ-Out

93. Drilling and re-taping
Half of the time an EZ-Out will not work
The next option is to keep enlarging the hole until the original threads just begin to be seen
Then a tap of the original diameter and pitch can be run through the hole to remove the remaining material

94. Visible thread lines
When you can just begin to see thread lines stop drilling

95. Apply pressure to the tap
Slowly rotate the tap while applying firm pressure to the tap handle or ratchet

96. Lubricate the tap
Spray a few drops of lubricant on the tap

97. 1 full turn in – ¼ turn out
Rotate 1 full turn then turn the tap backwards ¼ turn
This allows the metal filings to drop into the tap flutes
Repeat this process – 1 full turn in – ¼ turn out until the tap reaches the end of the threads

98. Restored threads
When the tap is removed blow out any metal chips and the threads should be as good as new