1. Chapter 11
Fasteners and Springs

2. Screw Threads Fasteners Transmitting power
Helix or conical spiral formed on the external surface of a shaft or the internal surface of a hole
Threads are used for:
Fasteners
Transmitting power
Adjusting locations (leveling)

3. Unified Thread Series
Developed to standardize threads so that there would be interchangeability
U.S. used American National System before 1949

4. Screw Thread Terminology
Axis-centerline of the cylindrical thread shape Body-portion of the screw left unthreaded Chamfer-angular relief at the last thread to help engagement Lead-the distance the thread travels in one revolution. Right hand thread-thread that engages when rotated clockwise (standard) Left hand thread-thread that engages when rotated counter-clockwise.

5. Die-tool used for cutting external threads Tap-tool used for cutting internal threads. Tap drill-size of the drill used to make a hole before the tapping operation (each thread size requires a specific tap drill size) Fit-range of thread tightness or looseness. Included Angle-angle between the sides of the threads.

6. Crest-top of external threads, bottom of internal threads Root-bottom of external threads, top of internal Depth of thread-distance from the crest to the root Major Diameter-size of the largest diameter on the thread Minor Diameter-size of the smallest diameter on the thread Pitch-the distance from a point on a thread form to the corresponding point on the next thread form Pitch diameter-diameter halfway between the major dia. and the minor dia.

7. Thread form-profile of a thread (shape) Thread series-groups of major diameters and pitches. Threads per inch-number of threads included in one inch of length

8. Thread Forms Unified Threads
Most common
Aka. Unified National
Several thread series:
UNC
UNF
UNEF

9. American National Old standard-pre 1949
Flat root compared to Unified National
Harder to make

10. Sharp V Forms a tight seal
Difficult to make without damaging the crests and roots
Was original U.S. standard
Not common

11. Metric Thread ISO standard for metric sizes
Similar shape to Unified National

12. Whitworth Threads Original British standard Developed in 1841
Only used for replacement parts

13. Square Threads Used to transmit power (not fasten)
Difficult to manufacture

14. Acme Threads Transmit power Replaced square threads
Used for screw jacks and vice threads

15. Buttress Threads
Used to transmit power in one direction

16. Dardelet Threads Used where self locking threads are required
Resistant to loosening under vibration

17. Rolled Threads A formed thread (not cut)
Used for electrical parts (light bulbs, sockets)

18. American National Standard Taper Pipe
Used for pipe fittings
Designed to be pressure tight

19. Thread Representaion
Different methods of showing threads on engineering drawings.
3 Methods

20. Detailed Thread Representation
Shows the true shape of the threads
Not commonly used because of the time needed to draw and computing time to model

21. Schematic Thread Representation
A simple way to graphically represent threads
Not commonly used any more

22. Simplified Thread Representation
Similar to schematic but shows more accurate information
Preferred method

23. How to draw simplified