Fasteners Chapter 5

1. FastenersChapter 5

2. Fasteners Objectives • Describe USC threaded-fastener measuring system • Describe metric threaded measuring system • Identify grade markings of threaded fasteners • List and describe common thread repair tools

3. Objectives • Identify and explain purpose of common nonthreaded fasteners • Explain importance of wire gauge sizes • Identify common types of electrical fasteners

4. Introduction • Automotive components are held together with fasteners • Much of a technician’s time is spent removing and installing fasteners • There are two basic groups • Threaded • Non-threaded

5. Threaded Fasteners • Most common type of fastener • Use spiral threads to wedge parts together • Fastener Sizing and Torquing • Must be correct strength and size • Must be replaced with like size and quality • Never install a heavier sheer pin to “fix” a problem

6. Threaded Fasteners • Screws • One of the most common threaded fasteners • Fits into a threaded hole • Different designs to meet attaching needs • Some require a wrench to install, others can be installed with screwdrivers • Often classed by shape of head

8. Threaded Fasteners • Bolts • Use a nut instead of a threaded hole • Usually goes through parts that don’t have threads • Most have hex-shaped head • Two different types • Standard • Torque-to-yield

9. Threaded Fasteners • Studs • Fastener with no head and threads on both ends • Nuts • Used with bolts and studs • Many different designs • Can be specialized to specific applications

11. Torque-to-Yield Bolt Installation • Follow all manufacturer instructions on torquing the bolt • Typically first two steps involve an actual ft.lbs reading on a torque meter

12. Torque-to-Yield Bolt Installation • Final step requires tightening the fastener a specified number of degrees • Greatly reduces effect of friction on torque readings

13. Threaded Fasteners • Washers • Often used to distribute loads • Prevent a nut from becoming loose • Prevent damage to a machined surface

14. Flat Spring Lock External tooth lock Internal tooth lock Washers

15. Nuts

17. Threaded Fasteners • U.S. (English) Thread Sizes • Manufactured to Unified System specifications in Fractions of an Inch • Threads can be course or fine depending on the number of threads per inch • Bolt size is determined by shank diameter, bolt length, and threads per inch

18. Bolt Identification (Cont’d)

19. Bolt Identification • Diameter • Measured across the threaded area • Thread pitch (English system) • The number of threads per inch • Thread pitch (Metric system) • The distance in millimeters between two adjacent threads

20. Metric Size Bolt Identification Example • A metric size bolt that is identified as 6mm x 30mm x 1.25mm: • Has a shank diameter of 6 millimeters. • Is 30 millimeters long from the bottom of the head to the end of the shank. • Has a distance of 1.25 millimeters between its threads.

21. Imperial Size Bolt Identification Example • An Imperial size bolt that is identified as 3/8" x 2" x 24: • Has a shank diameter of 3/8 inch. • Is 2 inches long from the bottom of the head to the end of the shank. • Has 24 threads per inch.

23. Threaded Fasteners • Metric Thread Sizes • Same basic measurements as U.S. (English) bolts • Pitch number differentiates between fine and coarse as opposed to NC or NF ratings

24. Measuring Devices (Cont’d) • Screw pitch gauge / Thread pitch gauge • Is used to determine thread pitch of a bolt or screw. • Machinist’s rule • Is usually used to measure items that don’t require extremely close tolerances, such as bolt lengths

28. Bolt Grade Markings • Customary (inch) bolts • Identification marks correspond to bolt strength. • Increasing numbers represent increasing strength. • Metric bolts • Identification class numbers correspond to bolt strength. • Increasing numbers represent increasing strength. • Metric and SAE size wrenches are not interchangeable.

29. Threaded Fasteners • Hardness and Strength • Strength is identified by grade markings on the bolt head • Standards are set by the Society of Automotive Engineers (SAE) • Tensile strength is amount of pressure the fastener can take before it breaks

30. Grade Markings

31. Threaded Fasteners • Fastener Torque • Must be tightened to the correct amount • Not enough torque causes fastener to loosen • Too much leads to breakage

32. Torque Wrenches

33. Thread Repair Tools • Tap and Die Set • Heilicoil • Thread Restorer and Chasers • Screw Extractor or EZ-Out (Brand Name)

34. Thread Repair Tools • Tap and Die Sets • Dies are used to make external threads • Taper taps must extend through hole to work properly • Bottoming taps thread to bottom of hole

35. Thread Repair Tools • Helicoils • Threaded device threads into a hole and provides internal threads for a bolt • Must be used in conjunction with a properly sized drill and tap

36. Heilicoil

37. Thread Repair Tools • Thread Restorers and Chasers • Restoring files are used to smooth and shape damaged threads • Thread chasers fit over the damaged thread like a fastener • Turned back and forth over damaged threads until repaired

38. Thread Restorer files

39. TAP

44. Screw Extractor-EZ Out

46. Nonthreaded Fasteners • Snap Rings • Often used to hold parts in place on a shaft • Made from high quality steel that retains its shape • Snap rings can be internal or external

48. Electrical Wire • Replacement wire must be at least as heavy as the wire being repaired • Always try to match wire color • Use diagrams to pinpoint wire purpose before repairing

49. Electrical Wire size

50. Wire Sizes