Thread Types & Profiles Guide
Selecting the correct thread profile is crucial for load bearing, sealing, and regional compatibility. Mixing thread types (e.g., NPT with BSPT) will result in leaks and stripped threads.
| Thread Designation | Thread Angle | Standard | Application & Details |
|---|---|---|---|
| Metric Coarse (M) | 60° | ISO 261 / ISO 262 | The most common thread type globally. Default for general machinery and construction. |
| Metric Fine (MF) | 60° | ISO 261 | Finer pitch than coarse. Provides higher tensile strength and better resistance to vibration. |
| UNC (Unified National Coarse) | 60° | ASME B1.1 | Standard inch-series coarse thread used widely in the USA for general fastening. |
| UNF (Unified National Fine) | 60° | ASME B1.1 | Inch-series fine thread. Used in automotive and aerospace for tighter tensioning. |
| NPT (National Pipe Taper) | 60° | ANSI B1.20.1 | Tapered thread used in North America for sealing pipes. Requires thread sealant (Teflon tape/dope). |
| BSPT (British Standard Pipe Taper) | 55° | ISO 7 | Tapered thread common in Europe and Asia. Not compatible with NPT due to different thread angle. |
Coarse vs. Fine Threads
Coarse Threads (M, UNC):
- Less likely to cross-thread during assembly.
- More tolerant to dirt and damage.
- Faster to assemble and disassemble.
- Better for brittle materials like cast iron or aluminum.
Fine Threads (MF, UNF):
- Higher tensile strength due to larger minor diameter.
- Greater resistance to loosening from vibration.
- Allows for finer tension adjustment.
- Requires tighter hole tolerances.