3-1/2” Bolt & Screw Dimensions: Diameter & Head Size
3-1/2″ bolt dimensions and screw sizes are specified for heavy industrial hydraulic systems, primary bridge anchors, and massive power plant infrastructure. This size have a 3.500″ nominal major diameter and is available in 3-1/2″-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 extreme-scale 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.
3-1/2-4 UNC Screw & Bolt – ANSI/ASME B1.1
Dimension
Size (in)
Min
Max
Major Diameter
3.461
3.4967
Pitch Diameter
3.3177
3.3343
Minor Diameter
Not specified
3.199
Threads Per Inch (TPI)
4
Major Diameter
3.4729
3.4967
Pitch Diameter
3.3233
3.3343
Minor Diameter
Not specified
3.199
Threads Per Inch (TPI)
4
Major Diameter
3.4762
3.5
Pitch Diameter
3.3293
3.3376
Minor Diameter
Not specified
3.2023
Threads Per Inch (TPI)
4
3-1/2-6 UN Screw & Bolt – ANSI/ASME B1.1
Dimension
Size (in)
Min
Max
Major Diameter
3.4789
3.4971
Pitch Diameter
3.3792
3.3888
Minor Diameter
Not specified
3.2986
Threads Per Inch (TPI)
6
Major Diameter
3.4818
3.5
Pitch Diameter
3.3845
3.3917
Minor Diameter
Not specified
3.3015
Threads Per Inch (TPI)
6
3-1/2-8 UN Screw & Bolt – ANSI/ASME B1.1
Dimension
Size (in)
Min
Max
Major Diameter
3.4824
3.4974
Pitch Diameter
3.4074
3.4162
Minor Diameter
Not specified
3.3486
Threads Per Inch (TPI)
8
Major Diameter
3.485
3.5
Pitch Diameter
3.4122
3.4188
Minor Diameter
Not specified
3.3512
Threads Per Inch (TPI)
8
3-1/2-12 UN Screw & Bolt – ANSI/ASME B1.1
Dimension
Size (in)
Min
Max
Major Diameter
3.4867
3.4981
Pitch Diameter
3.4376
3.444
Minor Diameter
Not specified
3.3989
Threads Per Inch (TPI)
12
Major Diameter
3.4886
3.5
Pitch Diameter
3.4411
3.4459
Minor Diameter
Not specified
3.4008
Threads Per Inch (TPI)
12
3-1/2-16 UN Screw & Bolt – ANSI/ASME B1.1
Dimension
Size (in)
Min
Max
Major Diameter
3.4889
3.4983
Pitch Diameter
3.4519
3.4577
Minor Diameter
Not specified
3.4239
Threads Per Inch (TPI)
16
Major Diameter
3.4906
3.5
Pitch Diameter
3.4551
3.4594
Minor Diameter
Not specified
3.4256
Threads Per Inch (TPI)
16
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.
