Threads and threading considerations


Reading Assignment

  • 29.1 Introduction to Thread Manufacturing
  • 29.2 Thread Making
  • 29.3 Internal Thread Cutting-Tapping
  • 29.4 Thread Milling
  • 29.5 Thread Grinding
  • 29.6 Thread Rolling
  • (10.3 – Allowance and Tolerance)



Functions of Threads

  • Fastening
  • Adjustment
  • Power Transmission

Thread Terminology

Importance of Pitch Diameter

Measuring pitch diameter

Thread Specifications

1.  Basic Major diameter (fraction or decimal) followed by a hyphen.
2.  Number of threads per inch
Relationship to pitch
Sharp V
4.  Series of the thread, followed by a hyphen
Graded Pitch Series
Constant Pitch Series
5.  Class of fit (1, 2, or 3)
6.  Designation as external (A) or internal (B)
7.  Indication of left-hand (LH)
8.  Indication of multiple thread (Double or triple)
9.  Thread length if not full
10.  Finish, etc.

Metric Threads

2 Groups of Threads

  • General Purpose
  • Fine

Metric Thread Note

  • M20 X 1.5 5g6g
    • M Metric Form
    • Basic Major Diameter
    • Pitch
    • Tolerance (Grade and Position)
      • See Chapter 10.3 – Allowance and Tolerance

Thread Manufacturing

Taps and Dies

Tap Drilling

Size of hole in relation to Major Diameter

Types of Taps

  • Taper, Plug, Bottoming
  • Forming Taps

Tap Sizes (Tolerance Designation H/L)


Other Thread Manufacturing Methods

  • Cutting Threads on a Lathe
  • Chasing Threads
  • Rolling Threads
  • Milling Threads
  • Grinding Threads

 Additional Resources

Screw Thread Forms Quiz Game


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