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Technical drawing of the thread cross-section 47.5 degree flank angle

Whitworth Instrument Thread

The Whitworth instrument thread is a British fine thread used for optical devices and in the watch industry. It is an inch thread with a flank angle of 47.5°. Reflecting its applications, the dimensions of the Whitworth instrument thread are very small, ranging between 0.010 inches (0.245 mm) and 0.100 inches (2.540 mm).

The Whitworth instrument thread has no thread designation; instead, the various dimensions are numbered. Thread numbers range from 10 to 100, with not every number assigned. From 20 onwards, the count is in two-step increments, and from 40 in five-step increments.

In the thread table below for the Whitworth instrument thread, the diameter is given in inches and mm. The pitch is also listed in mm as well as in threads per inch, where the values quickly reach multiples of 100 due to the dimensions of the Whitworth instrument thread. The core hole diameter is also listed. We are happy to manufacture dies and taps for the Whitworth instrument thread as a custom order upon request!

To the overview thread standards
Thread No.
Diameter outside inch
Diameter outside mm
Diameter Core hole mm
Gears per Inch
Pitch mm
Taps in our online-shop
Dies in our online-shop
10
0,010
0,254
0,173
400
0,064
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11
0,011
0,279
0,198
400
0,064
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12
0,012
0,305
0,212
350
0,073
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13
0,013
0,330
0,237
350
0,073
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14
0,014
0,356
0,247
300
0,085
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16
0,016
0,406
0,298
300
0,085
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17
0,017
0,432
0,302
250
0,102
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18
0,018
0,457
0,327
250
0,102
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19
0,019
0,483
0,353
250
0,102
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20
0,020
0,508
0,353
210
0,121
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22
0,022
0,559
0,404
210
0,121
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24
0,024
0,610
0,455
210
0,121
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26
0,026
0,660
0,480
180
0,141
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28
0,028
0,711
0,531
180
0,141
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30
0,030
0,762
0,581
180
0,141
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32
0,032
0,813
0,632
180
0,141
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34
0,034
0,864
0,647
150
0,169
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36
0,036
0,914
0,698
150
0,169
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38
0,038
0,965
0,694
120
0,212
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40
0,040
1,016
0,745
120
0,212
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45
0,045
1,143
0,872
120
0,212
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50
0,050
1,270
0,945
100
0,254
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55
0,055
1,397
1,072
100
0,254
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60
0,060
1,524
1,199
100
0,254
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65
0,065
1,651
1,245
80
0,318
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70
0,070
1,778
1,372
80
0,318
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75
0,075
1,905
1,499
80
0,318
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80
0,080
2,032
1,490
60
0,423
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85
0,085
2,159
1,617
60
0,423
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90
0,090
2,286
1,744
60
0,423
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95
0,095
2,286
1,636
50
0,508
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100
0,100
2,540
1,890
50
0,508
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