Metric trapezoidal thread (Tr)
The 30° thread of lead screws, vises, clamps and feeds. Enter the diameter and pitch to get every screw and nut diameter, the thread depth and the tool tip width.
Quick answer
Tr 20×4 per ISO 2901: clearance ac = 0.25 mm, thread depth h3 = 0.5P + ac = 2.25 mm, pitch diameter d2 = 18 mm, screw minor d3 = 15.5 mm, nut bore D1 = 16 mm, nut major D4 = 20.5 mm.
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- Screw (external)
- Major d
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- Pitch d2
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- Minor d3
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- Depth h3
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- Nut (internal)
- Major D4
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- Pitch D2
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- Minor D1 (bore)
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- Depth H4
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- Crest clearance ac
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- Radii R1 / R2, max
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- Tool tip width (max)
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- Lead
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- Helix angle at d2
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Cutting it on a lathe. A 30° tool with a flat tip no wider than calculated. Feed in along the flank (at 15°) or shift Z a little each pass — the trapezoidal tool tip is wide, and plunging radially over the full width chatters. Full screw depth is h3.
Helix angle. On coarse pitches it is noticeable (about 4° on Tr 20×4): increase the tool's side clearance on the leading side by that much, or the flank will rub.
Designation. Tr 40×7 — single start; Tr 40×14 (P7) — two starts, lead 14, pitch 7; LH at the end — left hand.
Common sizes
| Thread | d2 = D2 | d3 | D1 | D4 | h3 | ac | Tool tip |
|---|---|---|---|---|---|---|---|
| Tr 8×1.5 | 7.25 | 6.2 | 6.5 | 8.3 | 0.9 | 0.15 | 0.47 |
| Tr 10×2 | 9 | 7.5 | 8 | 10.5 | 1.25 | 0.25 | 0.6 |
| Tr 12×3 | 10.5 | 8.5 | 9 | 12.5 | 1.75 | 0.25 | 0.96 |
| Tr 14×3 | 12.5 | 10.5 | 11 | 14.5 | 1.75 | 0.25 | 0.96 |
| Tr 16×4 | 14 | 11.5 | 12 | 16.5 | 2.25 | 0.25 | 1.33 |
| Tr 18×4 | 16 | 13.5 | 14 | 18.5 | 2.25 | 0.25 | 1.33 |
| Tr 20×4 | 18 | 15.5 | 16 | 20.5 | 2.25 | 0.25 | 1.33 |
| Tr 22×5 | 19.5 | 16.5 | 17 | 22.5 | 2.75 | 0.25 | 1.7 |
| Tr 24×5 | 21.5 | 18.5 | 19 | 24.5 | 2.75 | 0.25 | 1.7 |
| Tr 26×5 | 23.5 | 20.5 | 21 | 26.5 | 2.75 | 0.25 | 1.7 |
| Tr 28×5 | 25.5 | 22.5 | 23 | 28.5 | 2.75 | 0.25 | 1.7 |
| Tr 30×6 | 27 | 23 | 24 | 31 | 3.5 | 0.5 | 1.93 |
| Tr 32×6 | 29 | 25 | 26 | 33 | 3.5 | 0.5 | 1.93 |
| Tr 36×6 | 33 | 29 | 30 | 37 | 3.5 | 0.5 | 1.93 |
| Tr 40×7 | 36.5 | 32 | 33 | 41 | 4 | 0.5 | 2.29 |
| Tr 44×7 | 40.5 | 36 | 37 | 45 | 4 | 0.5 | 2.29 |
| Tr 48×8 | 44 | 39 | 40 | 49 | 4.5 | 0.5 | 2.66 |
| Tr 50×8 | 46 | 41 | 42 | 51 | 4.5 | 0.5 | 2.66 |
| Tr 60×9 | 55.5 | 50 | 51 | 61 | 5 | 0.5 | 3.03 |
| Tr 70×10 | 65 | 59 | 60 | 71 | 5.5 | 0.5 | 3.39 |
| Tr 80×10 | 75 | 69 | 70 | 81 | 5.5 | 0.5 | 3.39 |
Dimensions in mm, nominal (no tolerances). Formulas and ac clearances: ISO 2901:1993 clause 7 and table 2 (official text: IS 7008-1:1999, identical, open at law.resource.org); designations: ISO 2902. The tool tip width is derived from the 30° profile geometry (0.366P − 0.536ac). Tolerance classes (7e, 7H etc.) are in ISO 2903.