Spiral shaped outer or inner grooves are usually used for fitting
External threads are found on the screw and internal threads on the nut.
Threads are manufactured according to different standards, where ISO standard M is the most common. The M stands for Metric.
Dimensions stated by this standard are
- d/D : Major diameter
- d1/D1 : Minor diameter
- d2/D2 : Pitch diameter
- h/H : Depth
- P : Pitch (how much a thread rises per revolution)
- β : Thread angle
You can also distinguish between coarse threading, M and fine threading MF which have different pitch.
For an M5 screw or nut, the number indicates the nominal diameter which is the same as or close to the Major diameter.