Threads - Non Standard¶
Metric V Thread Form¶
| Symbol | Description |
|---|---|
| D | Major diameter of internal thread |
| d | Major diameter of external thread |
| D₂ | Pitch diameter of internal thread |
| d₂ | Pitch diameter of external thread |
| D₁ | Minor diameter of internal thread |
| d₁ | Minor diameter of external thread |
| P | Pitch |
| H | Height of fundamental triangle |
Example Drawing Note¶
<Thread Form><Nominal Diameter> x <Pitch> - [Starts] ([lead])
Example:
M8.5 x 1 - 2 START (LEAD 2)
Rules of Thumb for 60 Degree Metric Threads¶
Where D is the nominal diameter, P is the pitch.
| Feature | Rule of thumb |
|---|---|
| Tap Drill (Cutting Tap) | Tap drill ≈ D − P |
| Internal Thread Relief | Relief Ø ≥ D + 0.2 mm, Depth ≈ 1 - 2P |
| External Thread Relief | Relief Ø ≤ D − 1.3P (approx) |
Metric Thread Forms¶
| Thread Form | Drawing Initial |
|---|---|
| ISO metric V (60°) | M |
| ISO metric trapezoidal | Tr |
| ISO metric round | Rd |
| ISO buttress (saw-tooth) | S |
| ISO pipe thread, parallel | G |
| ISO pipe thread, tapered | R (external), Rp (internal parallel), Rc (internal taper) |