About Threads

Basic terminology for threads

1. **Thread** – A helical structure used to convert rotational and linear movement or force.

2. **Pipe Thread** – Threads cut into pipes or fittings for sealing and connection.

3. **Tapered Thread** – Thread diameter decreases along the length (e.g., NPT).

4. **Parallel Thread** – Thread diameter remains constant (e.g., BSPP).

5. **Thread Pitch** – Distance between adjacent thread crests.

6. **Thread Crest** – Top surface of a thread.

7. **Thread Root** – Bottom surface between two threads.

8. **Flank** – Side surface connecting crest and root.

9. **Thread Angle** – Angle between thread flanks (e.g., 55° for BSP, 60° for NPT).

Common thread types for malleable cast iron pipe fittings

10. **NPT (National Pipe Taper)** – U.S. standard tapered thread for sealing without gaskets.  

11. **NPTF (National Pipe Taper Fuel)** – Dry-seal variant of NPT for leak-proof connections.  

12. **BSPT (British Standard Pipe Taper)** – British tapered thread (55° angle).  

13. **BSPP (British Standard Pipe Parallel)** – British parallel thread (requires sealant/washer).  

14. **G Thread** – ISO designation for BSPP (e.g., G1/2″).  

15. **R Thread** – ISO designation for BSPT (external taper).  

16. **Metric Thread** – Measured in millimeters (e.g., M20×1.5).