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FASTENERS

FASTENERS. FASTENERS. Fasteners Described by several factors: Material Head style Type Diameter Length Thread count. FASTENERS. Material Describes what the fastener is made from Some common examples: Stainless steel Steel Brass

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FASTENERS

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  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. FASTENERS • Sample chart:

  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:

  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 • Metric fasteners • 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 • 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 • 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 • Used to prevent nuts and bolts from backing out • Internal tooth washer • Identical to above except teeth are inside

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