3″ screw dimensions and bolt sizes are critical for bridge infrastructure, dam gate assemblies, and high-pressure industrial flanges. This size have a 3.000″ nominal major diameter and is available in 3″-4 coarse (UNC) thread pitch, representing 4 threads per inch (TPI). This reference chart follows ANSI/ASME B18.6.3 and B18.3 standards for the head size and ANSI/ASME B1.1 standards for the thread dimensions to ensure compatibility across massive imperial fastening applications.
Disclaimer: Dimensions and tolerances may vary slightly depending on head style, manufacturer, or material — always verify with the official product datasheet before use.
3-4 UNC Screw & Bolt – ANSI/ASME B1.1
Dimension
Size (in)
Min
Max
Major Diameter
2.9611
2.9968
Pitch Diameter
2.8183
2.8344
Minor Diameter
Not specified
2.6991
Threads Per Inch (TPI)
4
Major Diameter
2.973
2.9968
Pitch Diameter
2.8237
2.8344
Minor Diameter
Not specified
2.6991
Threads Per Inch (TPI)
4
Major Diameter
2.9762
3
Pitch Diameter
2.8296
2.8376
Minor Diameter
Not specified
2.7023
Threads Per Inch (TPI)
4
3-6 UN Screw & Bolt – ANSI/ASME B1.1
Dimension
Size (in)
Min
Max
Major Diameter
2.979
2.9972
Pitch Diameter
2.8796
2.8889
Minor Diameter
Not specified
2.7987
Threads Per Inch (TPI)
6
Major Diameter
2.9818
3
Pitch Diameter
2.8847
2.8917
Minor Diameter
Not specified
2.8015
Threads Per Inch (TPI)
6
3-8 UN Screw & Bolt – ANSI/ASME B1.1
Dimension
Size (in)
Min
Max
Major Diameter
2.9824
2.9974
Pitch Diameter
2.9077
2.9162
Minor Diameter
Not specified
2.8486
Threads Per Inch (TPI)
8
Major Diameter
2.985
3
Pitch Diameter
2.9124
2.9188
Minor Diameter
Not specified
2.8512
Threads Per Inch (TPI)
8
3-12 UN Screw & Bolt – ANSI/ASME B1.1
Dimension
Size (in)
Min
Max
Major Diameter
2.9867
2.9981
Pitch Diameter
2.9377
2.944
Minor Diameter
Not specified
2.8989
Threads Per Inch (TPI)
12
Major Diameter
2.9886
3
Pitch Diameter
2.9412
2.9459
Minor Diameter
Not specified
2.9008
Threads Per Inch (TPI)
12
3-16 UN Screw & Bolt – ANSI/ASME B1.1
Dimension
Size (in)
Min
Max
Major Diameter
2.9889
2.9983
Pitch Diameter
2.9521
2.9577
Minor Diameter
Not specified
2.9239
Threads Per Inch (TPI)
16
Major Diameter
2.9906
3
Pitch Diameter
2.9552
2.9594
Minor Diameter
Not specified
2.9256
Threads Per Inch (TPI)
16
3-20 UN Screw & Bolt – ANSI/ASME B1.1
Dimension
Size (in)
Min
Max
Major Diameter
2.9903
2.9984
Pitch Diameter
2.9607
2.9659
Minor Diameter
Not specified
2.9389
Threads Per Inch (TPI)
20
Major Diameter
2.9919
3
Pitch Diameter
2.9636
2.9675
Minor Diameter
Not specified
2.9405
Threads Per Inch (TPI)
20
Major Diameter –
The largest diameter of the external thread, measured crest to crest.
This defines the nominal size of the screw or bolt.
Pitch Diameter –
The diameter of an imaginary cylinder where the thread thickness equals
the space between threads. This dimension primarily controls thread fit
and tolerance class of 2A and 3A.
Minor Diameter –
The smallest diameter of the external thread, measured root to root.
This affects thread strength and clearance.
Threads Per Inch (TPI) –
The number of complete threads within one inch of thread length.
Higher TPI values indicate a finer thread pitch.
What is the difference between a bolt and a screw?
The difference is based on the intent of the fastener’s use; If the primary intent is for the fastener to pass through an unthreaded holes and be assembled with a nut, it is a Bolt. In this application, you usually hold the head and turn the nut to apply tension. But if the primary intent is for the fastener to be installed into a threaded (tapped) hole, it is a Screw. In this application, the connection is tightened by turning the head of the fastener itself.
