日本語

Printed from Kezuriba (kezuriba.net/en/threads/m24/)

M24×3

ISO metric coarse thread

Nominal diameter 24 mm, pitch 3 mm. Tap makers recommend slightly different drill sizes, so they are listed side by side.

Tap drill, rule of thumb (d − P)
21.00 mmMaker recommendations below
Minor diameter D1 range (6H)
20.752 – 21.252 mmKeep the hole inside this range[4][5][3]
Pitch diameter d2 (basic)
22.051 mmd2 = d − 0.649519P
M24 basic profile and dimensions (schematic)
external thread (bolt)major dia. d = 24pitch dia. d2 = 22.051minor dia. D1 = 20.7526H range 20.752–21.252 (tap drill target)P = 3H160°

Thread angle 60°. H1 (basic thread engagement) = 0.541266P = 1.624. The pitch diameter is where the thread ridge and groove are equally wide. For cutting taps, pick a drill that lands inside the 6H tolerance of the minor diameter D1. Enlarged to show the shape; proportions are not to scale.

⌀Tap drill size for cutting taps (maker recommendations)

For internal thread class 6H. Values as given in each maker’s technical data (mm).

MakerRecommended drillNotesSource
OSG21min. 20.8, 6H max. 21.25
[3]
Nachi (Nachi-Fujikoshi)21high-performance drill 21.1[5]
Yamawa21.1[4]
Calculate tapping RPM for this size →

Forming (roll) tap drill sizes differ by maker and product line; see the Japanese page for the table.

⌇Basic dimensions

Nominal (major) diameter d24
Pitch P3
Pitch diameter d2, D222.051
Basic minor diameter D1 (nut), d1 (bolt)20.752
Fundamental triangle height H = 0.866025P2.598
Basic engagement H1 = 0.541266P1.624

Basic dimensions are theoretical values without tolerance. Try other pitches with the thread dimension calculator.

⬡Bolt and nut sizes

ItemmmConfidence
Hex bolt width across flats s (ISO-based JIS, main body)36Agrees in 2+ sources[8][9][10]
Hex bolt width across flats s (old JIS, annex)361 source (reference)[11]
Hex nut width across flats s (ISO-based JIS, main body)36Agrees in 2+ sources[8][12]
Hex nut width across flats s (old JIS, annex)361 source (reference)[13]
Hex nut height m (style 1, max.)21.51 source (reference)[12]
Socket head cap screw head diameter dk (max.)36Agrees in 2+ sources[14][15][16][17]
Socket head cap screw head height k (max.)24Agrees in 2+ sources[14][16][17]
Hex socket size s (hex key size)19Agrees in 2+ sources[14][15][16][17][8]
Hex socket depth t (min.)12Agrees in 2+ sources[14][15][16][17]

⊙Clearance holes and counterbores

ItemmmConfidence
Clearance hole d′ for socket head cap screws26Agrees in 2+ sources[14][19]
Counterbore diameter D′ for socket head cap screws39Agrees in 2+ sources[14][19]
Counterbore depth H″ (head sits below the surface)25.5Agrees in 2+ sources[14][19]
Counterbore depth H′ (head slightly proud)22.5Agrees in 2+ sources[14][19]
Clearance hole, class 1 (JIS B 1001)251 source (reference)[18]
Clearance hole, class 2 (JIS B 1001)261 source (reference)[18]
Clearance hole, class 3 (JIS B 1001)281 source (reference)[18]
Spotface diameter for hex bolts and nuts (JIS B 1001)501 source (reference)[18]

Socket-head values are from the reference table of JIS B 1176; clearance-hole classes are from JIS B 1001. The two standards give different clearance holes for some sizes.

≋M24 fine threads

SizeD1 range (6H)Recommended drill (cutting tap)
M24×221.835 – 22.21OSG 22 / Nachi (Nachi-Fujikoshi) 22 / Yamawa 22.1
M24×1.522.376 – 22.676OSG 22.5 / Nachi (Nachi-Fujikoshi) 22.5 / Yamawa 22.6

📚Sources

Most sources are Japanese technical documents from the tap and fastener makers.

  1. iwata-fa.jp https://www.iwata-fa.jp/contents/assets/pdf/technicaldata/2022_tec_other_13.pdf
  2. nbk1560.com https://www.nbk1560.com/images/ja-JP/product/technical_data/meternezi_NBK/meternezi_NBK_1.…
  3. osg.co.jp https://www.osg.co.jp/media_dl/technical/file/drill_hole_size.pdf
  4. yamawa.com https://www.yamawa.com/Portals/0/images/download/holesize/jp/technical-contents-15.pdf
  5. nachi-fujikoshi.co.jp https://www.nachi-fujikoshi.co.jp/dcms_media/other/2501-12.pdf
  6. baer.tools https://baer.tools/en/blog/core-hole-dimensions-for-screw-taps-everything-you-need-to-know
  7. orist.jp https://www.orist.jp/technicalsheet/98015.PDF
  8. eg.aktio.co.jp https://www.eg.aktio.co.jp/wp-content/uploads/R3T_1-5_TONE_bolt_nimen.pdf
  9. jp.misumi-ec.com https://jp.misumi-ec.com/pdf/fa/2015/p1_2367.pdf
  10. mikipulley.co.jp https://www.mikipulley.co.jp/en/resources/standards-hex-bolt
  11. tsurugacorp.co.jp https://www.tsurugacorp.co.jp/img/usr/pdf/B00000.pdf
  12. fabory.com https://www.fabory.com/en-GB/p/01104240001
  13. static.nbk1560.com https://static.nbk1560.com/images/ja-JP/product/technical_data/rokkaku_nut_NBK/rokkaku_nut…
  14. jp.misumi-ec.com https://jp.misumi-ec.com/pdf/fa/2015/p1_2363.pdf
  15. tsurugacorp.co.jp https://www.tsurugacorp.co.jp/img/usr/pdf/A00000.pdf
  16. static.nbk1560.com https://static.nbk1560.com/images/ja-JP/product/technical_data/rokkaku_bolt_NBK/rokkaku_bo…
  17. farnell.com https://www.farnell.com/datasheets/11699.pdf
  18. static.nbk1560.com https://static.nbk1560.com/images/ja-JP/product/technical_data/boltana_zagurikei_NBK/bolta…
  19. nbk1560.com https://www.nbk1560.com/resources/other/article/technical-22-dimensions-of-holes-for-hexag…