1. Chapter 11 Threaded Fasteners
Two Basic types of fasteners: Permanent & removable
Permanent- Examples: Rivets & welds
Removable- Examples: bolts, screws, nuts, pins, rings keys
Standardization reduces the costs of fasteners
3 purposes
To hold parts together
To adjust
To transfer power

2. Screw Threads
Definition: a SCREW THREAD is a ridge of uniform section in the form of a helix on the external or internal surface of a cylinder
Definition: the PITCH of a thread P is the distance from a point on the thread form to the corresponding point on the next form, measured parallel to the axis
Definition: the LEAD L is the distance the threaded part would move parallel to the axis during one complete rotation in relation to a fixed mating part (the distance a screw would enter a threaded hole in one turn)

3. THREADED FASTENERS
SCREW THREAD TERMS

4. THREADED FASTENERS
THREAD FORMS

5. THREADED FASTENERS
THREAD FORMS

6. Three types of thread representation used on working drawings
Simplified
Detailed
Schematic

7. Right- and Left-Hand threads
Threads are assumed to be right hand unless otherwise designated
A bolt being threaded into a tapped hole would be turned in a right-hand (clockwise) direction

8. THREADED FASTENERS
RIGHT- AND LEFT-HAND THREADS

9. THREADED FASTENERS
LEAD = 1P
SINGLE THREAD

10. THREADED FASTENERS
LEAD = 2P
DOUBLE THREAD

11. THREADED FASTENERS
LEAD = 3P
TRIPLE THREAD

12. Inch Threads Definition: PITCH =1/#threads per inch
Definition: THREAD SERIES are for fasteners with different diameters and the same #threads per inch
UNC Unified Course Thread Series
UNF Unified Fine Thread Series (Table appendix)
UNEF extra fine thread series

13. THREADED FASTENERS
BASIC THREAD CALLOUT

14. Thread Class 1A,2A,3A External 1B,2B,3B Internal
1A,1B: loosest fit
2A,2B: ordinary good grade of commercial product
3A,3B: High-grade commercial products
Example: UNC-2A class of fit
Nominal Diameter thread series
#threads/inch
(Diameter, #threads/inch, thread form & series, class of fit)

15. THREADED FASTENERS
EXTERNAL THREADS

16. THREADED FASTENERS
BLIND HOLE
INTERNAL THREAD

17. Metric Threads
Definition: Pitch for metric threads is the distance between corresponding points on adjacent teeth.
Course-thread is intended for general engineering work and commercial applications
Fine-thread series is for general use. Compared with coarse, a fine-thread screw is stronger in both tensile and torsional strength
Definition: the FIT of a screw thread is the amount of clearance between the internal and external threads when they are assembled
Tolerance grades: the larger the number, the larger the tolerance
Tolerance position e (large allowance)
Tolerance position g (small allowance)
Tolerance position h (no allowance)
For internal threads:
Tolerance position G (small allowance)
Tolerance position H (no allowance)

18. THREADED FASTENERS
BASIC THREAD CALLOUT
METRIC THREADS

19. ISO Metric Screw Thread Designation
Nominal size (basic major diameter) and pitch expressed in millimeters.
Example: M16 x 1.5 – 5g6g
Metric designation Nominal diameter Pitch Tolerance position & grade
Example: M10 x 1.5 x 25
Ф10mm 1.5 pitch 25 mm long
Example: M16 (pitch may be omitted for coarse threads)

20. Metric Threads continued
For external threads, the length of the thread may be given as a dimension of the drawing.
For threaded holes that go all the way through the part, the term THRU is sometimes added
If no depth is given, the hole is assumed to go THRU
For threaded holes that do not go all the way thru, the depth is given in a note (minimum depth of full thread) Ex. M12 x 1.75 x 20

21. Pipe Threads Inch: 4-8NPT or 4 NPT Metric: 4 IN. – 8 NPT or 4 IN.-NPT
Nominal diameter and pipe thickness specify inch-sized pipe (typical)
4=nominal diameter
8=number of threads/inch
N=American Standard
P=pipe
S=straight pipe thread
T=taper pipe thread