3/4 - 12 12-UN - Basic Thread Dimensions

Property Inch mm
Nominal Diameter 0.75 19.05
Pitch (TPI)12
Pitch (Distance) 0.0833 2.116
Pitch Diameter 0.6959 17.676
Minor Diameter 0.6508 16.53
Thread Height 0.0451 1.146
Addendum 0.0271 0.688
Crest (External)
Root (Internal)		 0.0104 0.264
Tap Drill Size
(75% depth)		 0.669 16.99
Lead Angle
(Single Start)		 2.18°
Thread Family Unified Constant Pitch 6 TPI (12-UN)
Relevant Standards ASME B1.1-2003
Equivalent Metric ThreadM20 X 2

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

Table of Content

3/4 - 12 12-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

3/4 - 12 12-UN 2A (External)

* Permisable values for thread Class 2A

# Description Value (Inch) Value (mm)
es Allowance 0.0016 (Ref) 0.041 (Ref)
d Major Diameter 0.737 - 0.7484 18.72 - 19.009
d2 Pitch Diameter 0.6891 - 0.6943 17.503 - 17.635
d3 Minor Diameter
(UNR Only)		 0.6492 (Ref) 16.49 (Ref)
α Varation of 30° anngle (+/-) 0.9167°
P Varation of pitch (+/-) 0.0015 (Ref) 0.038 (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

3/4 - 12 12-UN 3A (External)

* Permisable values for thread Class 3A

# Description Value (Inch) Value (mm)
es Allowance 0 (Ref) 0 (Ref)
d Major Diameter 0.7386 - 0.75 18.76 - 19.05
d2 Pitch Diameter 0.692 - 0.6959 17.577 - 17.676
d3 Minor Diameter
(UNR Only)		 0.6508 (Ref) 16.53 (Ref)
α Varation of 30° anngle (+/-) 0.9167°
P Varation of pitch (+/-) 0.0011 (Ref) 0.028 (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

3/4 - 12 12-UN 2B (Internal)

* Permisable values for thread Class 2B

# Description Value (Inch) Value (mm)
D1 Minor Diameter 0.66 - 0.678 16.764 - 17.221
D2 Pitch Diameter 0.6959 - 0.7027 17.676 - 17.849
D Major Diameter 0.7500 (Min) 19.05 (Min)
α Varation of 30° anngle (+/-) 0.9167°
P Varation of Pitch (+/-) 0.0019 (Ref) 0.048 (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

3/4 - 12 12-UN 3B (Internal)

* Permisable values for thread Class 3B

# Description Value (Inch) Value (mm)
D1 Minor Diameter 0.6598 - 0.6707 16.759 - 17.036
D2 Pitch Diameter 0.6959 - 0.701 17.676 - 17.805
D Major Diameter 0.7500 (Min) 19.05 (Min)
α Varation of 30° anngle (+/-) 0.9167°
P Varation of Pitch (+/-) 0.0015 (Ref) 0.038 (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 3/4 - 12 12-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% 0.690 17.54
60% 0.685 17.40
65% 0.680 17.26
70% 0.674 17.12
75% 0.669 16.99
80% 0.663 16.85
85% 0.658 16.71

Over Wire Measurements for 3/4 - 12 12-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 0.0421 - 0.0842 1.069 - 2.138
Ideal Wire Diameter 0.0481 1.222
Possible Wires
From Standard Sets		 * 0.0642
* 0.0722
* 0.077
* 0.0825
 * 1.155
* 1.443
* 1.732
* 2.021

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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