1/2 - 16 16-UN - Basic Thread Dimensions

Property Inch mm
Nominal Diameter 0.5 12.7
Pitch (TPI)16
Pitch (Distance) 0.0625 1.588
Pitch Diameter 0.4594 11.669
Minor Diameter 0.4256 10.81
Thread Height 0.0338 0.859
Addendum 0.0203 0.516
Crest (External)
Root (Internal)
0.0078 0.198
Tap Drill Size
(75% depth)
0.439 11.15
Lead Angle
(Single Start)
2.48°
Thread Family Unified Constant Pitch 16 TPI (16-UN)
Relevant Standards ASME B1.1-2003
Equivalent Metric ThreadM12 X 1.5

For more threading data scroll down, or use the Thread Calculator

Table of Content


1/2 - 16 16-UN Possible Thread Classes

External Threads

Choose tolerance class: 2A, 3A

Metric ISO External Thread - Tolerance sketch

Internal Threads

Choose tolerance class: 2B, 3B

Metric ISO Internal Thread - Tolerance sketch

1/2 - 16 16-UN 2A (External)

* Permisable values for thread Class 2A

# Description Value (Inch) Value (mm)
es Allowance 0.0013 (Ref) 0.033 (Ref)
d Major Diameter 0.4893 - 0.4987 12.428 - 12.667
d2 Pitch Diameter 0.4537 - 0.4581 11.524 - 11.636
d3 Minor Diameter
(UNR Only)
0.4243 (Ref) 10.777 (Ref)
α Varation of 30° anngle (+/-)
P Varation of pitch (+/-) 0.0013 (Ref) 0.033 (Ref)

* Values are calculated for Length of engagement of 5xPitch. For calculations of different engagement length use the Thread Calculator

* Back to Thread Class Selection


1/2 - 16 16-UN 3A (External)

* Permisable values for thread Class 3A

# Description Value (Inch) Value (mm)
es Allowance 0 (Ref) 0 (Ref)
d Major Diameter 0.4906 - 0.5 12.461 - 12.7
d2 Pitch Diameter 0.4561 - 0.4594 11.585 - 11.669
d3 Minor Diameter
(UNR Only)
0.4256 (Ref) 10.81 (Ref)
α Varation of 30° anngle (+/-)
P Varation of pitch (+/-) 0.001 (Ref) 0.025 (Ref)

* Values are calculated for Length of engagement of 5xPitch. For calculations of different engagement length use the Thread Calculator

* Back to Thread Class Selection


1/2 - 16 16-UN 2B (Internal)

* Permisable values for thread Class 2B

# Description Value (Inch) Value (mm)
D1 Minor Diameter 0.432 - 0.446 10.973 - 11.328
D2 Pitch Diameter 0.4594 - 0.4651 11.669 - 11.814
D Major Diameter 0.5000 (Min) 12.7 (Min)
α Varation of 30° anngle (+/-)
P Varation of Pitch (+/-) 0.0016 (Ref) 0.041 (Ref)

* Values are calculated for Length of engagement of 5xPitch. For calculations of different engagement length use the Thread Calculator

* Back to Thread Class Selection


1/2 - 16 16-UN 3B (Internal)

* Permisable values for thread Class 3B

# Description Value (Inch) Value (mm)
D1 Minor Diameter 0.4323 - 0.4419 10.98 - 11.224
D2 Pitch Diameter 0.4594 - 0.4637 11.669 - 11.778
D Major Diameter 0.5000 (Min) 12.7 (Min)
α Varation of 30° anngle (+/-)
P Varation of Pitch (+/-) 0.0012 (Ref) 0.03 (Ref)

* Values are calculated for Length of engagement of 5xPitch. For calculations of different engagement length use the Thread Calculator

* Back to Thread Class Selection


Tap Drill Sizes for 1/2 - 16 16-UN

  • If not specified, assume a thread depth of 75%.
  • You can learn more about thread depth in tapping here.
  • To get the tap drill size in other depths, use our Tap Drill Size Calculator .
Thread Depth Tap Drill Size (Inch) Tap Drill Size (mm)
55% 0.455 11.56
60% 0.451 11.46
65% 0.447 11.36
70% 0.443 11.26
75% 0.439 11.15
80% 0.435 11.05
85% 0.431 10.95

Over Wire Measurements for 1/2 - 16 16-UN


* OverWire is a measuring method to obatin the pitch diameter of threads. It is mostly used when a manufacturer does not have a Go/Nogo gauge for a thread. You can learn more about it here

Inch mm
Permissible Wire Diameter Range 0.0316 - 0.0631 0.802 - 1.604
Ideal Wire Diameter 0.0361 0.917
Possible Wires
From Standard Sets
* 0.866
* 1.01
* 1.155
* 1.443

Once you knoe your wire diameter, you need to find out what is the premissable Measurement for your pitch diameter (Depending on the class). Use our Over Wire Calculator to find out!


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