2. 8 Screw Thread Representation

3. Permission granted to reproduce for educational use only. Define terms related to screw threads and fasteners. Identify common screw thread forms. Describe three methods for representing screw threads. Discuss screw thread characteristics that may affect the specification.

4. Permission granted to reproduce for educational use only. Explain the different parts of a screw thread specification or callout. Discuss the differences between metric threads and inch threads. Identify standard pipe thread representation and designations.

5. Permission granted to reproduce for educational use only. Thread Terms and Definitions External thread Internal thread Crest Root Major diameter Minor diameter Pitch diameter Pitch Lead

6. Permission granted to reproduce for educational use only. Thread Terms and Definitions

7. Permission granted to reproduce for educational use only. Thread Forms

8. Permission granted to reproduce for educational use only. Thread Representation

9. Permission granted to reproduce for educational use only. Unified Screw Thread Series Unified coarse (UNC) Unified fine (UNF) Unified extra fine (UNEF) Other less common specifications: –Unified constant-pitch (UN) –Unified with rounded root (UNR and UNJ) –Unified special or non-standard (UNS)

10. Permission granted to reproduce for educational use only. Multiple Threads Called multiple-start threads (two start, three start) In the past, called double or triple threads

11. Permission granted to reproduce for educational use only. Reverse Threads Right-hand threads are common Left-hand threads are called reverse threads

12. Permission granted to reproduce for educational use only. Specification of Screw Threads

13. Permission granted to reproduce for educational use only. Metric Threads

14. Permission granted to reproduce for educational use only. Pipe Threads Pipe thread designations: –NPT: general use –NPTR: railing joints –NPSC: couplings –NPTF: Dryseal –NPSF: fuel (internal)

15. Permission granted to reproduce for educational use only.

16. What is the difference between the root and the crest of a screw thread? The root is the bottom of the thread between two ridges and the crest is the top edge of a ridge.

17. Permission granted to reproduce for educational use only. List at least four common thread forms. Unified, Acme, stub Acme, buttress, pipe, and Dryseal

18. Permission granted to reproduce for educational use only. What are the three methods of representing screw threads on a drawing? Detailed, simplified, and schematic

19. Permission granted to reproduce for educational use only. What four characteristics of a screw thread may appear in the specification on a drawing (not the size dimension)? Thread series, thread class, multiple thread, and left-hand thread

20. Permission granted to reproduce for educational use only. What information appears first in a screw thread specification for inch-based thread? Nominal diameter

21. Permission granted to reproduce for educational use only. How does the thread specification for metric thread differ from that for inch-based thread? The specification begins with M followed by diameter  pitch.

22. Permission granted to reproduce for educational use only. What are the three forms of pipe thread used in industry? Regular, aeronautical, and Dryseal