日本語

Printed from Kezuriba (kezuriba.net/en/threads/m2-5/)

M2.5×0.45

ISO metric coarse thread

Nominal diameter 2.5 mm, pitch 0.45 mm. Tap makers recommend slightly different drill sizes, so they are listed side by side.

Tap drill, rule of thumb (d − P)
2.05 mmMaker recommendations below
Minor diameter D1 range (6H)
2.013 – 2.138 mmKeep the hole inside this range[4][5][3]
Pitch diameter d2 (basic)
2.208 mmd2 = d − 0.649519P
M2.5 basic profile and dimensions (schematic)
external thread (bolt)major dia. d = 2.5pitch dia. d2 = 2.208minor dia. D1 = 2.0136H range 2.013–2.138 (tap drill target)P = 0.45H160°

Thread angle 60°. H1 (basic thread engagement) = 0.541266P = 0.244. 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
OSG2.05min. 2.02, 6H max. 2.13
previous edition recommended 2.08 (changed in the current edition)		[3]
Nachi (Nachi-Fujikoshi)2.05high-performance drill 2.1[5]
Yamawa2.11[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 d2.5
Pitch P0.45
Pitch diameter d2, D22.208
Basic minor diameter D1 (nut), d1 (bolt)2.013
Fundamental triangle height H = 0.866025P0.390
Basic engagement H1 = 0.541266P0.244

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)51 source (reference)[10]
Hex bolt width across flats s (old JIS, annex)—Not confirmed
Hex nut width across flats s (ISO-based JIS, main body)5Agrees in 2+ sources[10][11]
Hex nut width across flats s (old JIS, annex)51 source (reference)[12]
Hex nut height m (style 1, max.)21 source (reference)[11]
Socket head cap screw head diameter dk (max.)4.5Agrees in 2+ sources[13][14][15][16]
Socket head cap screw head height k (max.)2.5Agrees in 2+ sources[13][15][16]
Hex socket size s (hex key size)2Agrees in 2+ sources[13][14][15][16][10]
Hex socket depth t (min.)1.1Agrees in 2+ sources[13][14][15][16]

⊙Clearance holes and counterbores

ItemmmConfidence
Clearance hole d′ for socket head cap screws—Not confirmed
Counterbore diameter D′ for socket head cap screws—Not confirmed
Counterbore depth H″ (head sits below the surface)—Not confirmed
Counterbore depth H′ (head slightly proud)—Not confirmed
Clearance hole, class 1 (JIS B 1001)—Not confirmed
Clearance hole, class 2 (JIS B 1001)—Not confirmed
Clearance hole, class 3 (JIS B 1001)—Not confirmed
Spotface diameter for hex bolts and nuts (JIS B 1001)—Not confirmed

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.

📚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. osg.co.jp https://www.osg.co.jp/media_dl/technical/file/p_8.pdf
  7. yamawa.com https://www.yamawa.com/Portals/0/images/download/holesize/jp/technical-contents-16.pdf
  8. baer.tools https://baer.tools/en/blog/core-hole-dimensions-for-screw-taps-everything-you-need-to-know
  9. orist.jp https://www.orist.jp/technicalsheet/98015.PDF
  10. eg.aktio.co.jp https://www.eg.aktio.co.jp/wp-content/uploads/R3T_1-5_TONE_bolt_nimen.pdf
  11. fabory.com https://www.fabory.com/en-GB/p/01103025001
  12. static.nbk1560.com https://static.nbk1560.com/images/ja-JP/product/technical_data/rokkaku_nut_NBK/rokkaku_nut…
  13. jp.misumi-ec.com https://jp.misumi-ec.com/pdf/fa/2015/p1_2363.pdf
  14. tsurugacorp.co.jp https://www.tsurugacorp.co.jp/img/usr/pdf/A00000.pdf
  15. static.nbk1560.com https://static.nbk1560.com/images/ja-JP/product/technical_data/rokkaku_bolt_NBK/rokkaku_bo…
  16. mikipulley.co.jp https://www.mikipulley.co.jp/EN/Services/Tech_data/tech10.html