Relief Grooves & Chamfer Standards
DIN 509 relief groove forms E/F/G/H with dimensions and tolerances, GB/T 3 and DIN 76 thread undercuts, and chamfer sizes with the C-notation drawing rules.
DIN 509 relief grooves — forms E, F, G and H (mm)
| Form | r | t1 | t2 | f | g | Workpiece diameter d1 (mm) | Duty |
|---|---|---|---|---|---|---|---|
| E | 0.2 | 0.1 | — | 1 | — | 1.6 to 3 | Normal |
| E | 0.4 | 0.2 | — | 2 | — | 3 to 18 | Normal |
| E | 0.6 | 0.2 | — | 2 | — | 10 to 18 | Normal |
| E | 0.6 | 0.3 | — | 2.5 | — | 18 to 80 | Normal |
| E | 0.8 | 0.3 | — | 2.5 | — | 18 to 80 | Normal |
| E | 1.0 | 0.2 | — | 2.5 | — | 18 to 50 | Higher alternating |
| E | 1.0 | 0.4 | — | 4 | — | over 80 | Normal |
| E | 1.2 | 0.2 | — | 2.5 | — | 18 to 50 | Higher alternating |
| E | 1.2 | 0.4 | — | 4 | — | over 80 | Normal |
| E | 1.6 | 0.3 | — | 4 | — | 50 to 80 | Higher alternating |
| E | 2.5 | 0.4 | — | 5 | — | 80 to 125 | Higher alternating |
| E | 4.0 | 0.5 | — | 7 | — | over 125 | Higher alternating |
| F | 0.2 | 0.1 | 0.1 | 1 | 0.9 | 1.6 to 3 | Normal |
| F | 0.4 | 0.2 | 0.1 | 2 | 1.1 | 3 to 18 | Normal |
| F | 0.6 | 0.2 | 0.1 | 2 | 1.4 | 10 to 18 | Normal |
| F | 0.6 | 0.3 | 0.2 | 2.5 | 2.1 | 18 to 80 | Normal |
| F | 0.8 | 0.3 | 0.2 | 2.5 | 2.3 | 18 to 80 | Normal |
| F | 1.0 | 0.2 | 0.1 | 2.5 | 1.8 | 18 to 50 | Higher alternating |
| F | 1.0 | 0.4 | 0.3 | 4 | 3.2 | over 80 | Normal |
| F | 1.2 | 0.2 | 0.1 | 2.5 | 2.0 | 18 to 50 | Higher alternating |
| F | 1.2 | 0.4 | 0.3 | 4 | 3.4 | over 80 | Normal |
| F | 1.6 | 0.3 | 0.2 | 4 | 3.1 | 50 to 80 | Higher alternating |
| F | 2.5 | 0.4 | 0.3 | 5 | 4.8 | 80 to 125 | Higher alternating |
| F | 4.0 | 0.5 | 0.3 | 7 | 6.4 | over 125 | Higher alternating |
| G | 0.4 | 0.2 | 0.2 | 0.9 | 1.1 | 3 to 18 | Low fatigue loads only |
| H | 0.8 | 0.3 | 0.05 | 2.0 | 1.1 | 18 to 80 | Normal |
| H | 1.2 | 0.3 | 0.05 | 2.4 | 1.5 | 18 to 50 | Normal |
How to read this table. Tolerances: r ±0.1; t1 +0.1/0; t2 +0.05/0; f +0.2/0. Form E is for parts where only the cylindrical face is finished; form F where two perpendicular faces are both finished; form G for small included angles; form H for large included angles. Grinding relief grooves on Chinese drawings fall under GB/T 6403.5-2008 (values not reproduced here).
Thread Undercut, External — GB/T 3-1997
Chinese drawings. The undercut diameter d8 carries tolerance h13 (h12 where the thread diameter is 3 mm or below), and the transition angle α is not less than 30°. For European drawings use the DIN 76 table further down — the two systems do not mix.
| Pitch P (mm) | g2 max | g1 min | d8 | r |
|---|---|---|---|---|
| 0.5 | 1.5 | 0.8 | d − 0.8 | 0.2 |
| 0.7 | 2.1 | 1.1 | d − 1.1 | 0.4 |
| 0.8 | 2.4 | 1.3 | d − 1.3 | 0.4 |
| 1.0 | 3.0 | 1.6 | d − 1.6 | 0.6 |
| 1.25 | 3.75 | 2.0 | d − 2.0 | 0.6 |
| 1.5 | 4.5 | 2.5 | d − 2.3 | 0.8 |
| 1.75 | 5.25 | 3.0 | d − 2.6 | 1.0 |
| 2.0 | 6.0 | 3.4 | d − 3.0 | 1.0 |
| 2.5 | 7.5 | 4.4 | d − 3.6 | 1.2 |
| 3.0 | 9.0 | 5.2 | d − 4.4 | 1.6 |
Thread Undercut, Internal — GB/T 3-1997
Internal thread relief. The undercut diameter D5 carries tolerance H13, and G1 is given in a normal and a short version — pick one and state it on the drawing.
| Pitch P (mm) | G1 normal | G1 short | D5 | R |
|---|---|---|---|---|
| 0.5 | 2 | 1 | D + 0.3 | 0.2 |
| 0.7 | 2.8 | 1.4 | D + 0.4 | 0.4 |
| 0.8 | 3.2 | 1.6 | D + 0.4 | 0.4 |
| 1.0 | 4 | 2 | D + 0.5 | 0.5 |
| 1.25 | 5 | 2.5 | D + 0.6 | 0.6 |
| 1.5 | 6 | 3 | D + 0.8 | 0.8 |
| 1.75 | 7 | 3.5 | D + 0.9 | 0.9 |
| 2.0 | 8 | 4 | D + 1.0 | 1.0 |
| 2.5 | 10 | 5 | D + 1.2 | 1.2 |
| 3.0 | 12 | 6 | D + 1.5 | 1.5 |
Thread Undercut — DIN 76-1 (European drawings)
Forms: A external regular, B external short, C internal regular, D internal short. The current edition is DIN 76-1:2025-10; the values below follow the 2016 edition and should be verified against the purchased standard text before release. Do not mix GB/T 3 and DIN 76 on the same drawing: for M10 both give an undercut diameter of 7.7 mm with r = 0.8, but the widths differ (GB g2 = 4.5, DIN form A g = 5.2).
| Thread | P | dg external (h13) | r | dG internal (H13) | g, form A | g, form B | g, form C | g, form D |
|---|---|---|---|---|---|---|---|---|
| M3 | 0.5 | 2.2 | 0.2 | 3.3 | 1.75 | 1.25 | 2.7 | 2.0 |
| M4 | 0.7 | 2.9 | 0.4 | 4.3 | 2.45 | 1.75 | 3.8 | 2.75 |
| M5 | 0.8 | 3.7 | 0.4 | 5.3 | 2.8 | 2.0 | 4.2 | 3.0 |
| M6 | 1.0 | 4.4 | 0.6 | 6.5 | 3.5 | 2.5 | 5.2 | 3.7 |
| M8 | 1.25 | 6.0 | 0.6 | 8.5 | 4.4 | 3.2 | 6.7 | 4.9 |
| M10 | 1.5 | 7.7 | 0.8 | 10.5 | 5.2 | 3.8 | 7.8 | 5.6 |
| M12 | 1.75 | 9.4 | 1.0 | 12.5 | 6.1 | 4.3 | 9.1 | 6.1 |
| M14 | 2.0 | 11.0 | 1.0 | 14.5 | 7.0 | 5.0 | 10.3 | 7.3 |
| M16 | 2.0 | 14.4 | 1.2 | 18.5 | 8.7 | 6.3 | 13.0 | 9.3 |
Chamfer Sizes and Drawing Indication
The C prefix is only for 45° equal-leg chamfers: C1 means 1 mm axially and 1 mm radially. A non-45° chamfer must show angle and length separately (GB/T 4458.4). The GB/T 6403.4 size series for R and C values is: 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.8, 1.0, 1.2, 1.6, 2.0, 2.5, 3.0, 4.0, 5.0, 6.0, 8.0, 10, 12, 16, 20, 25, 32, 40, 50.
| Scenario | Common chamfers | Drawing indication | Tolerance convention |
|---|---|---|---|
| External diameter | C0.5, C1, C1.5, C2 | 45° written as C1 or 1×45°; non-45° chamfers show angle and length separately. | ISO 2768-m broken edges: 0.5–3 ±0.2; 3–6 ±0.5; over 6 ±1.0 |
| Internal bore | C0.5, C1, C2 | On the entry edge; the same C rules apply as outside. | ISO 2768-1 broken-edge rows, same as external |
| End face | C1, C2, C3 | Equal-leg C notation only at 45°. | Per the ISO 2768 class stated in the title block |
| Thread end, external | See the thread chamfer table below | 45° typical, 30°/60° allowed; depth at least the thread profile height. | Transition angle α ≥ 30° (GB/T 3-1997 clause 2.3) |
| Thread entry, internal | See the thread chamfer table below | 120° included angle typical, 90° allowed; diameter (1.0–1.05) × D. | Countersink, not a linear C dimension (GB/T 3-1997 clause 3.3) |
Thread-End Chamfers M3–M24
External threads chamfer at 45° to at least the profile height (0.5413 × P). The tip diameters in the derived column are arithmetic values (d − 1.08P), not published standard values; the shop-rule column is the simplification d − P. Internal threads countersink at 120° included to 1.0–1.05 × D. The chamfer exists so the go gauge rides in and the first thread is not damaged.
| Thread | P | External angle | Tip dia, derived (d − 1.08P) | Shop rule (d − P) | Internal countersink | Internal dia | Purpose |
|---|---|---|---|---|---|---|---|
| M3 | 0.5 | 45° | 2.46 ≈ 2.5 | 2.5 | 120° | 3.0–3.15 | Guides the die or tap; protects the first thread. |
| M4 | 0.7 | 45° | 3.24 ≈ 3.2 | 3.3 | 120° | 4.0–4.2 | Eases assembly start. |
| M5 | 0.8 | 45° | 4.14 ≈ 4.1 | 4.2 | 120° | 5.0–5.25 | Removes the first-crest burr. |
| M6 | 1.0 | 45° | 4.92 ≈ 4.9 | 5.0 | 120° | 6.0–6.3 | Nut and bolt engagement lead-in. |
| M8 | 1.25 | 45° | 6.65 ≈ 6.6 | 6.75 | 120° | 8.0–8.4 | Protects the load-bearing first turns. |
| M10 | 1.5 | 45° | 8.38 ≈ 8.4 | 8.5 | 120° | 10.0–10.5 | Prevents cross-threading. |
| M12 | 1.75 | 45° | 10.11 ≈ 10.1 | 10.25 | 120° | 12.0–12.6 | Assembly lead-in. |
| M14 | 2.0 | 45° | 11.84 ≈ 11.8 | 12.0 | 120° | 14.0–14.7 | Protects the first full thread. |
| M16 | 2.0 | 45° | 13.84 ≈ 13.8 | 14.0 | 120° | 16.0–16.8 | Die entry and burr control. |
| M18 | 2.5 | 45° | 15.30 | 15.5 | 120° | 18.0–18.9 | Thread-start protection. |
| M20 | 2.5 | 45° | 17.30 | 17.5 | 120° | 20.0–21.0 | Prevents galling at the start. |
| M22 | 2.5 | 45° | 19.30 | 19.5 | 120° | 22.0–23.1 | Assembly lead-in. |
| M24 | 3.0 | 45° | 20.76 ≈ 20.8 | 21.0 | 120° | 24.0–25.2 | Protects the first load-bearing turns. |
How to Use These Numbers
- A missing relief groove kills the assembly datum: without one at a bearing shoulder, the grinding wheel cannot exit, the corner keeps a radius, the inner ring never seats against the shoulder — and the axial location fails.
- C1 and 1×45° are equivalent only at 45°. The moment the angle changes to 30°, writing C1 is wrong: the C prefix means a 45° equal-leg chamfer, and non-45° chamfers take separate angle and length callouts (GB/T 4458.4).
- The internal thread entry is a 120° included angle at 1.0–1.05 × D. Calling it 60° invites the shop to read a single-side 60°; write the included angle and the diameter, and never draw the countersink diameter equal to the tap drill.
- Relief grooves and mating-part counterbores must match: DIN 509 also gives the mating counterbore dimension a (minimum 0.6 for a 0.8 × 0.3 groove, for example). Skip it and the mating face fouls the groove wall before it seats.
- Do not mix the standards on export drawings: for M10 external thread, GB/T 3 gives groove width g2 = 4.5 mm while DIN 76 form A gives g = 5.2 mm (both with an undercut diameter of 7.7 mm and r = 0.8). Whichever standard the title block names, use that table exclusively.
Frequently Asked Questions
What undercut do I need for a ground M10 external thread?
GB/T 3-1997 (P = 1.5): g2 = 4.5, d8 = 7.7, r = 0.8. European drawings use DIN 76 form A: g = 5.2, dg = 7.7, r = 0.8. The two systems are not interchangeable.
GB/T 3-1997 (P = 1.5): g2 = 4.5, d8 = 7.7, r = 0.8. European drawings use DIN 76 form A: g = 5.2, dg = 7.7, r = 0.8. The two systems are not interchangeable.
What does C2 mean on a drawing?
A 45° equal-leg chamfer, 2 mm axially and 2 mm radially, per GB/T 4458.4-2003.
A 45° equal-leg chamfer, 2 mm axially and 2 mm radially, per GB/T 4458.4-2003.
What chamfer angle for an internal metric thread entry?
120° included angle, countersink diameter 1.0–1.05 × D, per GB/T 3-1997 clause 3.3.
120° included angle, countersink diameter 1.0–1.05 × D, per GB/T 3-1997 clause 3.3.
What chamfer size for an M12 external thread end?
45°, with depth at least the profile height (0.5413 × 1.75 = 0.95 mm); derived tip diameter about 10.1 mm, and the shop rule d − P gives 10.25 mm.
45°, with depth at least the profile height (0.5413 × 1.75 = 0.95 mm); derived tip diameter about 10.1 mm, and the shop rule d − P gives 10.25 mm.
Which DIN 509 form for a low-fatigue shoulder?
Form G is restricted to low fatigue loads. For a normal-duty shoulder on an 18–80 mm diameter, form E with r = 0.8, t1 = 0.3, f = 2.5 is the usual pick.
Form G is restricted to low fatigue loads. For a normal-duty shoulder on an 18–80 mm diameter, form E with r = 0.8, t1 = 0.3, f = 2.5 is the usual pick.
What tolerance applies to an unmarked C1 chamfer under ISO 2768-m?
±0.2 mm — broken edges fall in the 0.5–3 mm nominal range of ISO 2768-1.
±0.2 mm — broken edges fall in the 0.5–3 mm nominal range of ISO 2768-1.
Which relief groove for two perpendicular faces that both need finishing?
DIN 509 form F; the typical pick on an 18–80 mm diameter is r = 0.8, t1 = 0.3, t2 = 0.2, f = 2.5.
DIN 509 form F; the typical pick on an 18–80 mm diameter is r = 0.8, t1 = 0.3, t2 = 0.2, f = 2.5.
Can I annotate a 30° chamfer with the C prefix?
No. Per GB/T 4458.4, non-45° chamfers require separate angle and length indications — the C prefix is reserved for 45° equal-leg chamfers.
No. Per GB/T 4458.4, non-45° chamfers require separate angle and length indications — the C prefix is reserved for 45° equal-leg chamfers.
Standards & Sources
- DIN 509:2022-12 — relief grooves, forms E/F/G/H (dimension values per the 2006 English full text, carried into the current edition)
- DIN EN ISO 18388:2016 — relief grooves for turning (ISO counterpart; note there is no K form in DIN 509)
- GB/T 3-1997 — bolts, screws, studs and nuts: thread runouts, shoulder distances, undercuts and chamfers
- DIN 76-1:2025-10 — thread undercuts (values below follow the 2016 edition; verify against the purchased text)
- GB/T 6403.4-2008 — parts rounding and chamfering (R/C size series)
- GB/T 4458.4-2003 — drawing indication rules for chamfers
- ISO 2768-1 — general tolerances for linear dimensions (broken-edge tolerance rows)
- GB/T 6403.5-2008 — grinding relief grooves (values not verified in this study; not reproduced)
- Thread-end tip diameters (d − 1.08P) are arithmetic derivations from the 0.5413 × P profile height, listed separately from standard published values
Related Pages
- /wiki/reference/grooving-parting-widths/ — Sibling quick table: which insert width cuts the groove
- /wiki/reference/thread-tap-drill-sizes/ — Tap drill sizes for the same thread range
- /wiki/reference/standard-tolerances/ — ISO 2768 general tolerances, including the broken-edge rows used for chamfers
- /wiki/threads/thread-types/ — Thread types and thread designations on machined parts