日本語

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

UNC / UNF tap drill sizes

For Unified inch threads (coarse UNC and fine UNF), the number/letter drills common in the US are listed next to the recommended tap drill in mm. TPI is threads per inch; pitch in mm = 25.4 ÷ TPI.

⌀Tap drills for cut taps

SizeTPIMajor dia. mmMinor dia. 2B mmDrill (no./letter/in)OSG mmYamawa mm
#4-40 UNC402.8452.157–2.385#430.089 in2.272.33
#4-48 UNF482.8452.271–2.458#420.0935 in2.372.41
#6-32 UNC323.5052.642–2.895#360.1065 in2.772.83
#6-40 UNF403.5052.82–3.022#330.113 in2.922.97
#8-32 UNC324.1663.302–3.53#290.136 in3.423.47
#8-36 UNF364.1663.404–3.606#290.136 in3.513.56
#10-24 UNC244.8263.683–3.962#250.1495 in3.813.89
#10-32 UNF324.8263.963–4.165#210.159 in4.074.11
1/4-20 UNC206.354.979–5.257#70.201 in5.125.19
1/4-28 UNF286.355.36–5.588#30.213 in5.475.53
5/16-18 UNC187.9386.401–6.731F0.257 in6.576.65
5/16-24 UNF247.9386.782–7.035I0.272 in6.916.97
3/8-16 UNC169.5257.798–8.1535/160.3125 in7.988.06
3/8-24 UNF249.5258.382–8.636Q0.332 in8.518.57
7/16-14 UNC1411.1129.144–9.55U0.368 in9.359.4
7/16-20 UNF2011.1129.729–10.03325/640.3906 in9.889.96
1/2-13 UNC1312.710.592–11.02327/640.4219 in10.8110.9
1/2-20 UNF2012.711.329–11.60729/640.4531 in11.4711.54
5/8-11 UNC1115.87513.386–13.86817/320.5312 in13.613.7
5/8-18 UNF1815.87514.351–14.68137/640.5781 in14.514.6
3/4-10 UNC1019.0516.307–16.8421/320.6562 in16.616.7
3/4-16 UNF1619.0517.323–17.67811/160.6875 in17.517.59
1-8 UNC825.421.971–22.6067/80.875 in22.322.4
1-12 UNF1225.423.114–23.57159/640.9219 in23.423.5

Number and letter drills are from the YG-1 chart (with expected thread engagement); mm values are from the technical data of OSG Japan (recommendations per JIS B 1004-1975) and Yamawa. The two makers differ by up to about 0.1 mm; we show both rather than pick one. Shaded rows are UNF.

Unified thread profile, and pitch from TPI
60°P5H/8Thread angle 60°, H = 0.866PFlat crest P/8, root P/4 (external)Same basic profile as ISO metric;only sizes differ (inches and TPI)Pitch P (mm) = 25.4 ÷ TPIThreads in 1 inch (25.4 mm) = TPI (same scale)1 inchUNCUNF1/4-20 UNC: 20 threads → P = 25.4 ÷ 20 = 1.27 mm1/4-28 UNF: 28 threads → P = 25.4 ÷ 28 ≈ 0.907 mm

“1/4-20” means 1/4 in major diameter and 20 threads per inch. UNF (fine) has more threads per inch for the same diameter, so a finer pitch. The two bars are drawn at the same scale.

◎Tap drills for form (roll) taps

SizeOSG New Roll Tap (range)Yamawa (tap class G7)
#4-40 UNC2.52–2.62.64
#4-48 UNF2.57–2.64—
#6-32 UNC3.09–3.173.21
#6-40 UNF3.19–3.26—
#8-32 UNC3.75–3.833.86
#8-36 UNF3.8–3.88—
#10-24 UNC4.26–4.354.4
#10-32 UNF4.41–4.484.51
1/4-20 UNC5.66–5.765.82
1/4-28 UNF5.86–5.935.97
5/16-18 UNC7.18–7.297.33
5/16-24 UNF7.38–7.46—
3/8-16 UNC8.66–8.78—
3/8-24 UNF8.96–9.059.07
7/16-14 UNC10.11–10.25—
7/16-20 UNF10.44–10.54—
1/2-13 UNC11.62–11.78—
1/2-20 UNF12.02–12.12—
5/8-11 UNC14.62–14.76—
5/8-18 UNF15.14–15.25—
3/4-10 UNC17.67–17.88—
3/4-16 UNF18.22–18.32—
1-8 UNC23.65–23.84—
1-12 UNF24.28–24.41—

In mm. Form tap drill sizes depend on the maker and the tap class.

📚Sources

  1. res.cloudinary.com https://res.cloudinary.com/osg-usa-inc/image/upload/v1717093846/Literature/03%20-%20Charts…
  2. yg1usa.com https://yg1usa.com/feature/item_view.asp?disp=2-33&cat_id=3&sub_id=31&sub_sub_id=399
  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. nbk1560.com https://www.nbk1560.com/images/ja-JP/product/technical_data/unifi_namime_NBK/unifi_namime_…
  6. yamawa.com https://www.yamawa.com/Portals/0/images/download/holesize/jp/technical-contents-16.pdf