Example designation
1/8-27 NPSL
- 1/8
- Nominal pipe size.
- 27
- Threads per inch.
- NPSL
- Straight locknut pipe thread family.
One bound can be the whole requirement
The external major diameter has an upper limit, and the internal minor diameter has a lower limit. Their opposite bounds are unspecified here; a midpoint or full tolerance band cannot be inferred from them.
Use the pitch-diameter interval
Both external and internal pitch diameters have minimum and maximum limits. These are the complete intervals to compare when reviewing the screw and locknut fit; the external measurement uses three wires.