Threads - Non Standard¶
Example Drawing Note¶
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M8.5 x 1 - 2 START (LEAD 2)
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<Thread Form><Nominal Diameter> x <Pitch> - [Starts] ([lead])
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) |