1. FASTENERS

2. FASTENERS Fasteners Described by several factors: Material Head style
Type
Diameter
Length
Thread count

3. FASTENERS Material Describes what the fastener is made from
Some common examples:
Stainless steel
Steel
Brass
Special coatings may also be added, such as zinc, in order to prevent corrosion or enhance appearance

4. FASTENERS Head style Describes the type of head on the fastener
Selected depending upon the purpose of the fastener
Common head styles:
Flat
Oval
Pan
Truss
Round
Hex

5. FASTENERS Type Designates the purpose of the fastener
Some common types:
Wood screw
Machine screw
Sheet metal screw
Self drilling or self tapping
Hex bolt
Carriage bolt
Lag bolt
Set screw

6. FASTENERS
Diameter is expressed in inches with the exception of small screws
Expressed as a size number preceded by the # sign (i.e. #12)
Differing size numbers correspond with fractional measurements
A complete chart can be found in most handy reference guides

7. Nearest Fractional Measurement
FASTENERS
Sample chart:
Size Number
Decimal
Nearest Fractional Measurement #0
.060
1/16 #5
.125
1/8
#10
.190
3/16
#12
.216
7/32

8. FASTENERS
Diameter is normally measured as shank diameter except in the case of tapered screws, such as wood screws, where the root is measured instead
Length is normally expressed in inches and is measured from where the material surface is assumed to be (the end of the fastener)
If the fastener head sits above the surface, the measurement is measured directly under the head of the fastener

9. FASTENERS
If the fastener is designed to be countersunk, the measurement is made from the point on the head where the surface of the material is
Thread count
Expressed as Threads Per Inch (TPI)
Simply means the number of threads per inch measured along the length of the fastener
Used only with American fasteners
Only applies to machine threads
In general, smaller fasteners have finer threads, therefore the thread count will be higher

10. FASTENERS
The relationship between a fastener size (diameter) and the number of threads per inch is standardized in a series
Two most common United States thread series:
UNC (or NC) – Unified Course Thread (commonly called course)
UNF (or NF)– Unified Fine Thread (commonly called fine)
A complete table for these series can be found in most handy reference guides

11. FASTENERS Sample table: Fastener Size UNC (tpi) UNF (tpi) #1 64 72 #1024 32 ¼” 20 28
3/8” 14 ½” 12 ¾” 10 16 1” 8

12. FASTENERS
Bolt grade
One final factor that should be considered when dealing with bolts is grade
Bolt grade is designated by numbers on the bolt head
The following are common grades of bolts:
Grade 2
Steel
Most common
Least expensive
Have no head markings

13. FASTENERS
Grade 5
Case hardened steel (outside only is hardened)
Not as strong as a fully hardened bolt
Designated by three evenly spaced radial lines on the head
Grade 8
Fully hardened steel
Very hard but somewhat brittle
More likely to snap off rather than bend under extreme load
Designated by 6 evenly spaced radial lines

14. FASTENERS
Alloy steel
High strength steel alloy
Heat treated
Typically not plated resulting in a dull black finish
Extremely strong, but very brittle
It is important to have all physical factors (especially thread count) or the fastener will not fit properly
This also applies to any corresponding nut

15. FASTENERS Thread pitch Metric fasteners Distance between threads
Described similarly to American fasteners (material, head style, type)
Use thread pitch rather than thread count
Thread pitch
Distance between threads
Expressed in millimeters (measured along the length of the fastener)
Example: a thread pitch of 1.5 means that the distance between one thread and the next is 1.5mm

16. FASTENERS Nuts and washers
Different thread pitch designations similar to American fasteners:
Standard
Fine
Extra or super fine
Nuts and washers
Fasteners have numerous accessories to accompany them and it is just as important to replace these items at the same time

17. FASTENERS The following are common nuts and their uses: Hex nut
Nylon insert lock nut
Has a nylon insert to prevent backing off
Also referred to as a Nylock
Jam nut
Hex nut with reduced height
Wing nut
Has wings for hand tightening
Cap or Acorn nut
Has a domed top over the end of the fastener

18. FASTENERS Flange nut Kep nut Square nut Non-reversable
A nut with a built in washer
Kep nut
A nut with a built in external tooth lock washer
Used to speed up assembly
Square nut
Prevailing torque lock nut
Non-reversable
Used for high-temperature applications

19. FASTENERS The following are common washer types and their uses: Flat
Used to distribute load
Fender
Oversized flat washer
Better distributes load especially on soft materials
Finishing
Used for a finished appearance
Used with oval head screws
Split lock
Most common style
Used to prevent nuts and bolts from backing out

20. FASTENERS External tooth lock Internal tooth washer
Used to prevent nuts and bolts from backing out
Internal tooth washer
Identical to above except teeth are inside

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