Threads
ISO metric threads (M): coarse and fine pitch sizes
ISO metric threads are 60° V-threads designated by M, the major diameter in millimetres and, for fine pitches, the pitch in millimetres (M12 is coarse, M12×1.25 is fine). The same thread is published by ISO, CEN, BSI, BIS and JIS, and as ASME B1.13M in the USA, so an M12 bolt from any of these regions fits an M12 nut from any other.
Names by standard
Standards in each region
| Region | System | Designation | תקן | Match |
|---|---|---|---|---|
| USA | ASME metric M profile | M12×1.75-6gUS publication of the ISO metric thread. Basic profile and coarse pitches agree with ISO; ASME writes the pitch even for coarse threads. | ASME B1.13M | Equivalent |
| UK | BS EN ISO / BS | M12BS 3643 gives ISO metric thread principles and limits of size; fastener standards are published as BS EN ISO. | BS 3643-1 and BS 3643-2 | Same material |
| EU | ISO metric (EN ISO) | M12, M12×1.25ISO 68-1 basic profile, ISO 261 general plan, ISO 262 selected sizes for bolts and nuts, ISO 724 basic dimensions, ISO 965 tolerances. Germany also cites DIN 13. | ISO 68-1, ISO 261, ISO 262, ISO 724, ISO 965 | Same material |
| הודו | IS 4218 | M12Indian publication of the ISO general-purpose metric thread series; Part 3 gives basic dimensions. | IS 4218 (Parts 1–4) | Same material |
| Japan | JIS | M12Japanese publication of ISO 68-1, 261, 262 and 724. JIS pitches were aligned with ISO in 1967; some older Japanese fine pitches differ. | JIS B 0205-1 to -4 | Same material |
Thread form
גיאומטריה
- Thread angle
- 60°, symmetric V
- Pitch expressed as
- Millimetres between adjacent threads
- Fundamental triangle height (H)
- 0.866 × pitch
- Basic thread depth
- 5/8 H, about 0.541 × pitch
- Designation
- M + major diameter (mm); add ×pitch only for fine pitches, e.g. M16×1.5
- Common tolerance classes
- 6g external, 6H internal (ISO 965)
- Hand
- Right-hand unless LH is added
Size chart
Common sizes
| מידה | Major diameter (mm) | Coarse pitch (mm) | Common fine pitch (mm) | Tap drill, coarse (mm) |
|---|---|---|---|---|
| M3 | 3 | 0.5 | 0.35 | 2.5 |
| M4 | 4 | 0.7 | 0.5 | 3.3 |
| M5 | 5 | 0.8 | 0.5 | 4.2 |
| M6 | 6 | 1 | 0.75 | 5.0 |
| M8 | 8 | 1.25 | 1 or 0.75 | 6.8 |
| M10 | 10 | 1.5 | 1.25 or 1 | 8.5 |
| M12 | 12 | 1.75 | 1.5 or 1.25 | 10.2 |
| M14 | 14 | 2 | 1.5 | 12.0 |
| M16 | 16 | 2 | 1.5 | 14.0 |
| M18 | 18 | 2.5 | 2 or 1.5 | 15.5 |
| M20 | 20 | 2.5 | 2 or 1.5 | 17.5 |
| M22 | 22 | 2.5 | 2 or 1.5 | 19.5 |
| M24 | 24 | 3 | 2 | 21.0 |
| M27 | 27 | 3 | 2 | 24.0 |
| M30 | 30 | 3.5 | 2 | 26.5 |
| M33 | 33 | 3.5 | 2 | 29.5 |
| M36 | 36 | 4 | 3 | 32.0 |
Tap drill uses the common workshop rule: major diameter minus coarse pitch, which gives roughly 75–80% thread engagement. Fine pitches are the combinations listed for screws, bolts and nuts; ISO 261 allows further pitches. Second-choice sizes (M14, M18, M22, M27, M33) are less widely stocked than the first-choice sizes.
In practice
Uses and compatibility
Where it is used
- General-purpose bolts, screws, studs and nuts worldwide
- Threaded rods and studding (normally coarse pitch)
- Anchor bolts and foundation bolts
- Fine pitches for adjusting screws, thin-walled parts and where vibration resistance or fine adjustment matters
- Automotive and machine components
What interchanges
- M-threads are interchangeable across ISO, EN ISO, BS, IS, JIS and ASME B1.13M publications when size, pitch and tolerance class match.
- Coarse and fine pitches of the same diameter do not mate: an M12 (1.75 mm) bolt will not run into an M12×1.25 nut.
- Metric threads do not interchange with UNC or UNF. Near-misses such as M8 (1.25 mm) and 5/16-18 UNC (7.94 mm, 1.41 mm pitch) may start by hand and then bind or strip.
- Metric threads do not interchange with BSW, BSF or pipe threads, which use a 55° angle and inch-based pitches.
תשובות לשאלות
Common questions
What is the pitch of M12?
M12 coarse has a 1.75 mm pitch, and that is what plain "M12" means. The common fine pitches are 1.5 mm and 1.25 mm, written M12×1.5 and M12×1.25.
What size drill do I need to tap M10?
Use an 8.5 mm drill for M10 coarse (1.5 mm pitch). The rule is major diameter minus pitch: 10 − 1.5 = 8.5 mm.
What is the difference between metric coarse and fine threads?
Fine threads have a smaller pitch for the same diameter, so they have a larger stress area and allow finer adjustment. Coarse threads assemble faster, tolerate dirt and damage better and are the default for bolts, nuts and threaded rod.
Is a Japanese or Indian M10 bolt the same as a European M10?
Yes. JIS B 0205 and IS 4218 publish the ISO metric thread, so an M10 coarse bolt from Japan or India fits an M10 coarse nut made to ISO or EN ISO standards.
What does 6g or 6H mean on a metric thread?
They are ISO 965 tolerance classes. 6g is the usual class for external threads such as bolts, and 6H is the usual class for internal threads such as nuts.
From the Corona catalog
Products listed with ISO metric (M)
בורג מכונה / בורג ראש מרובע
קוטר: 3/8-1 1/4 in (נפוצים: 1/2, 5/8, 3/4 in) / M10-M32 · אורך: 2-40 in / 50-1000 mm
מפרט טכני
זרוע לתיל דוקרני
מידה: עמוד: 14 G x 1-5/8, 1-7/8, 2, 2-3/8, 2-1/2 in / — · סוג: זרוע 45° ל-3 גדילים, זרוע אנכית ל-3 גדילים, זרוע V ל-6 גדילים
מפרט טכני
בורג סגר
מידה: 1/4-1/2 in (5/16 ו-3/8 in לאביזרי גדר) / M6-M12 · אורך: 1-1/4-12 in / 25-300 mm
מפרט טכני
מוטות הברגה / מוטות מוברגים
קוטר: 1/4" - 2-1/2" / M6 - M60 · אורך: 2 ft - 19 ft (נפוצים: 3, 6, 10, 12 ft) / 1 m - 5.8 m (נפוצים: 1, 2, 3 m)
מפרט טכניKeep reading
Related references
References
Sources
- ISO metric screw thread (Wikipedia, summarising ISO 68-1, 261, 262, 724, 965) — Coarse and fine pitches, tap drill rule, 1967 JIS alignment.
- BSI: BS 3643-1:2007 ISO metric screw threads, principles and basic data — UK standard status.
- BSI: BS 3643-2 ISO metric screw threads, selected limits of size
- BIS: IS 4218 (Part 3):1999 ISO general purpose metric screw threads, basic dimensions
- JIS screw thread standards list (JIS B 0205-1 to -4, B 0209)
- ASME B1.13M Metric screw threads: M profile — US publication of the ISO metric thread.
Values summarize published limits and typical data. The governing standard and the current edition control; check them before specifying.