Thread Bottom Hole & Outer Diameter Chart

Ever puzzled by which drill bit size matches your threading needs? This guide on thread bottom hole and outer diameter charts offers a comprehensive look at metric and imperial specifications. From understanding the right reference, minimum, and maximum hole diameters, this article ensures your machining tasks are precise and efficient. Dive in to learn how to achieve the perfect fit for your screws and bolts, ensuring every project is a success.

Thread Bottom Hole & Outer Diameter Chart

Table Of Contents

Thread Bottom Hole & Outer Diameter Chart

Metric Coarse Thread Bottom Hole Diameter

Thread SpecificationReference Hole DiameterMinimum Hole DiameterMaximum Hole Diameter (in MM)
M 1  × 0.250.750.7290.785
1.1 × 0.250.850.8290.885
1.2 × 0.250.950.9290.985
1.4 × 0.31.11.0751.142
1.6 × 0.351.251.2211.321
1.8 × 0.351.451.4211.521
2  × 0.41.61.5671.679
2.2 × 0.451.751.7131.838
2.5 × 0.452.12.0132.138
3  × 0.52.52.4592.599
3.5 × 0.62.92.853.01
4  × 0.73.33.2423.422
4.5 × 0.753.83.6883.878
5  × 0.84.24.1344.334
6  × 154.9175.153
7  × 165.9176.153
8  × 1.256.86.6476.912
9  × 1.257.87.6477.912
10  × 1.58.58.3768.676
11  × 1.59.59.3769.676
12  × 1.7510.310.10610.441
14  × 21211.83512.21
16  × 21413.83514.21
18  × 2.515.515.29415.744
20  × 2.517.517.29417.744
22  × 2.519.519.29419.744
24  × 32120.75221.252
27  × 32423.75224.252
30  × 3.526.526.21126.771
33  × 3.529.529.21129.771
36  × 43231.6732.27

Imperial Thread Bottom Diameter Chart

Thread SpecificationReference Hole DiameterMinimum Hole DiameterMaximum Hole Diameter (in MM)
NO.1  -64UNC1.551.4251.582
   2  -561.81.6951.871
3  -482.11.9412.146
4  -402.32.1572.385
   5  -402.62.4872.697
   6  -322.82.6422.895
   8  -323.43.3023.53
  10  -243.93.6833.962
  12  -244.54.3444.597
1/4-20 tooth5.14.9795.257
5/16  -186.66.4016.731
 3/8  -1687.7988.153
7/16  -149.49.1449.55
 1/2  -1310.810.59211.023
 9/16  -1212.211.98912.446
 5/8  -1113.613.38613.868
 3/4  -1016.516.30716.84
  7/8  – 919.519.17719.761
1inch-822.221.97122.606

Imperial Fine Thread Inner Hole Diameter Chart

Thread SpecificationReference Hole DiameterMinimum Hole DiameterMaximum Hole Diameter (in MM)
1  -721.551.4741.612
2  -641.851.7561.912
3  -562.12.0252.197
    4  -482.42.2712.458
    5  -442.72.5512.74
    6  -402.92.823.022
    8  -363.53.4043.606
   10  -324.13.9634.165
   12  -284.64.4964.724
1/4–285.55.365.588
5/16  -246.96.7827.035
3/8–24 tooth8.58.3828.636
 7/16 -209.99.72910.033
 1/2  -2011.511.32911.607
 9/16  -1812.912.75113.081
 5/8  -1814.514.35114.681
  3/4  -1617.517.32317.678
7/8–1420.520.2720.675
1 inch-1223.223.11423.571

Metric Fine Thread and Other Thread Pitch Bottom Diameter Chart

Thread SpecificationReference Hole DiameterMinimum Hole DiameterMaximum Hole Diameter (in MM)
M 2.5 × 0.352.22.1212.221
3  × 0.352.72.6212.721
3.5 × 0.353.23.1213.221
4  × 0.53.53.4593.599
4.5 × 0.543.9594.099
5  × 0.54.54.4594.599
5.5 × 0.554.9595.099
6  × 0.755.35.1885.378
7  × 0.756.36.1886.378
8  × 176.9177.153
8  × 0.757.37.1887.378
9  × 187.9178.153
9  × 0.758.38.1888.378
10  × 1.258.88.6478.912
10  × 198.9179.153
10  × 0.759.39.1889.378
11  × 1109.91710.153
11  × 0.7510.310.18810.378
12  × 1.510.510.37610.676
12  × 1.2510.810.64710.912
12  × 11110.91711.153
14  × 1.512.512.37612.676
14  × 11312.91713.153
15  × 1.513.513.37613.676
15  × 11413.91714.153
16  × 1.514.514.37614.676
16  × 11514.91715.153

Metric External Thread Outer Diameter Chart

Like the inner diameter of the thread, the outer diameter also has its standards. Some users may unnecessarily mark the tolerance on the outer diameter of the thread (except for those with specific usage requirements for the outer diameter). Below is the outer diameter chart for metric coarse thread, in MM.

Metric External Thread 60° Standard Coarse Thread Outer Diameter Chart:

SpecificationsPitchExternal Thread DiameterThread Rolling Diameter
MaxMin±0.02
M1.40.31.381.341.16
M1.70.351.681.611.42
M2.00.41.981.891.68
M2.30.42.282.191.98
M2.50.452.482.382.15
M3.00.52.982.882.6
M3.50.63.473.363.02
M4.00.73.983.833.4
M4.50.754.474.363.88
M5.00.84.984.834.3
M6.015.975.825.18
M7.016.976.826.18
M8.01.257.967.797.02
M9.01.258.968.798.01
M101.59.969.778.84
M111.510.9710.739.84
M121.7511.9511.7610.7
M141.7513.9513.7412.5
M16215.9515.7414.5
M18217.9517.7116.2
M202.519.9519.7118.2

This standard references GB9145-88, note that it is a “reference,” not equivalent to GB9145. The standards listed in this table are slightly higher than GB9145.”

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Shane
Author

Shane

Founder of MachineMFG

As the founder of MachineMFG, I have dedicated over a decade of my career to the metalworking industry. My extensive experience has allowed me to become an expert in the fields of sheet metal fabrication, machining, mechanical engineering, and machine tools for metals. I am constantly thinking, reading, and writing about these subjects, constantly striving to stay at the forefront of my field. Let my knowledge and expertise be an asset to your business.

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