#3 - 56 UNF - Basic Thread Dimensions

Property Inch mm
Nominal Diameter 0.099 2.515
Pitch (TPI)56
Pitch (Distance) 0.0179 0.455
Pitch Diameter 0.0874 2.22
Minor Diameter 0.0777 1.974
Thread Height 0.0097 0.246
Addendum 0.0058 0.147
Crest (External)
Root (Internal)
0.0022 0.056
Tap Drill Size
(75% depth)
0.082 2.07
Lead Angle
(Single Start)
3.73°
Thread Family Unified Fine Pitch (UNF)
Relevant Standards ASME B1.1-2003
Equivalent Metric ThreadM2.5

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

Table of Content


#3 - 56 UNF 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 - 56 UNF 2A (External)

* Permisable values for thread Class 2A

# Description Value (Inch) Value (mm)
es Allowance 0.0007 (Ref) 0.018 (Ref)
d Major Diameter 0.0942 - 0.0983 2.393 - 2.497
d2 Pitch Diameter 0.0845 - 0.0867 2.146 - 2.202
d3 Minor Diameter
(UNR Only)
0.0771 (Ref) 1.958 (Ref)
α Varation of 30° anngle (+/-) 2.25°
P Varation of pitch (+/-) 0.0006 (Ref) 0.015 (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 - 56 UNF 3A (External)

* Permisable values for thread Class 3A

# Description Value (Inch) Value (mm)
es Allowance 0 (Ref) 0 (Ref)
d Major Diameter 0.0949 - 0.099 2.41 - 2.515
d2 Pitch Diameter 0.0858 - 0.0874 2.179 - 2.22
d3 Minor Diameter
(UNR Only)
0.0777 (Ref) 1.974 (Ref)
α Varation of 30° anngle (+/-) 2.25°
P Varation of pitch (+/-) 0.0005 (Ref) 0.013 (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 - 56 UNF 2B (Internal)

* Permisable values for thread Class 2B

# Description Value (Inch) Value (mm)
D1 Minor Diameter 0.0797 - 0.0867 2.024 - 2.202
D2 Pitch Diameter 0.0874 - 0.0902 2.22 - 2.291
D Major Diameter 0.0990 (Min) 2.515 (Min)
α Varation of 30° anngle (+/-) 2.25°
P Varation of Pitch (+/-) 0.0008 (Ref) 0.02 (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 - 56 UNF 3B (Internal)

* Permisable values for thread Class 3B

# Description Value (Inch) Value (mm)
D1 Minor Diameter 0.0797 - 0.0865 2.024 - 2.197
D2 Pitch Diameter 0.0874 - 0.0895 2.22 - 2.273
D Major Diameter 0.0990 (Min) 2.515 (Min)
α Varation of 30° anngle (+/-) 2.25°
P Varation of Pitch (+/-) 0.0006 (Ref) 0.015 (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 - 56 UNF

  • 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% 0.086 2.19
60% 0.085 2.16
65% 0.084 2.13
70% 0.083 2.10
75% 0.082 2.07
80% 0.080 2.04
85% 0.079 2.01

Over Wire Measurements for #3 - 56 UNF


* 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 0.009 - 0.0181 0.23 - 0.459
Ideal Wire Diameter 0.0103 0.262
Possible Wires
From Standard Sets
* 0.0103
* 0.0116
* 0.012
* 0.0131
* 0.0144
* 0.016
* 0.018
* 0.231
* 0.26
* 0.289
* 0.346
* 0.404
* 0.433

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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