1-1/2” Bolt Dimensions: Thread, Diameter & Head Size

1-1/2″ bolt dimensions and screw sizes are usually used for massive industrial anchoring, heavy-duty machinery bases, and high-strength structural engineering. This size have a 1.500″ nominal major diameter and is available in 1-1/2″-6 coarse (UNC), 1-1/2″-12 fine (UNF), or 1-1/2″-18 extra-fine (UNEF) thread pitches, representing 6, 12, and 18 threads per inch (TPI) respectively. 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 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.

Thread diagram fot bolt and screw depicting the major diameter, minor diameter, pitch diameter, and threads per inch
Hex head diagram
Cap head diagram
Low-cap head diagram
Button head diagram
Flat head diagram
Pan head diagram
1-1/2-6 UNC Screw & Bolt – ANSI/ASME B1.1
Dimension Size (in)
Min Max
Major Diameter 1.4703 1.4976
Pitch Diameter 1.3772 1.3893
Minor Diameter Not specified 1.2991
Threads Per Inch (TPI) 6
Major Diameter 1.4794 1.4976
Pitch Diameter 1.3812 1.3893
Minor Diameter Not specified 1.2991
Threads Per Inch (TPI) 6
Major Diameter 1.4818 1.5
Pitch Diameter 1.3856 1.3917
Minor Diameter Not specified 1.3015
Threads Per Inch (TPI) 6
1-1/2-8 UN Screw & Bolt – ANSI/ASME B1.1
Dimension Size (in)
Min Max
Major Diameter 1.4828 1.4978
Pitch Diameter 1.4093 1.4166
Minor Diameter Not specified 1.349
Threads Per Inch (TPI) 8
Major Diameter 1.485 1.5
Pitch Diameter 1.4133 1.4188
Minor Diameter Not specified 1.3512
Threads Per Inch (TPI) 8
1-1/2-12 UNF Screw & Bolt – ANSI/ASME B1.1
Dimension Size (in)
Min Max
Major Diameter 1.4809 1.4981
Pitch Diameter 1.4344 1.444
Minor Diameter Not specified 1.3989
Threads Per Inch (TPI) 12
Major Diameter 1.4867 1.4981
Pitch Diameter 1.4376 1.444
Minor Diameter Not specified 1.3989
Threads Per Inch (TPI) 12
Major Diameter 1.4886 1.5
Pitch Diameter 1.4411 1.4459
Minor Diameter Not specified 1.4008
Threads Per Inch (TPI) 12
1-1/2-16 UN Screw & Bolt – ANSI/ASME B1.1
Dimension Size (in)
Min Max
Major Diameter 1.489 1.4984
Pitch Diameter 1.4526 1.4578
Minor Diameter Not specified 1.424
Threads Per Inch (TPI) 16
Major Diameter 1.4906 1.5
Pitch Diameter 1.4555 1.4594
Minor Diameter Not specified 1.4256
Threads Per Inch (TPI) 16
1-1/2-18 UNEF Screw & Bolt – ANSI/ASME B1.1
Dimension Size (in)
Min Max
Major Diameter 1.4898 1.4985
Pitch Diameter 1.4574 1.4624
Minor Diameter Not specified 1.4323
Threads Per Inch (TPI) 18
Major Diameter 1.4913 1.5
Pitch Diameter 1.4602 1.4639
Minor Diameter Not specified 1.4338
Threads Per Inch (TPI) 18
1-1/2-20 UN Screw & Bolt – ANSI/ASME B1.1
Dimension Size (in)
Min Max
Major Diameter 1.4905 1.4986
Pitch Diameter 1.4613 1.4661
Minor Diameter Not specified 1.4391
Threads Per Inch (TPI) 20
Major Diameter 1.4919 1.5
Pitch Diameter 1.4639 1.4675
Minor Diameter Not specified 1.4405
Threads Per Inch (TPI) 20
1-1/2-28 UN Screw & Bolt – ANSI/ASME B1.1
Dimension Size (in)
Min Max
Major Diameter 1.4922 1.4987
Pitch Diameter 1.4713 1.4755
Minor Diameter Not specified 1.4562
Threads Per Inch (TPI) 28
Major Diameter 1.4935 1.5
Pitch Diameter 1.4737 1.4768
Minor Diameter Not specified 1.4575
Threads Per Inch (TPI) 28
  • 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.
Hex Head – ANSI/ASME B18.2.1
Dimension Size (in)
MinMax
Width Across Flats 2.175 2.25
Width Across Corners 2.48 2.598
Head Height 0.902 1.036
Hex Socket Cap Head – ANSI/ASME B18.3
Dimension Size (in)
MinMax
Head Diameter 2.224 2.25
Head Height 1.485 1.5
Hex Socket Size 1 (1 in)
Hex Socket Flat Head – ANSI/ASME B18.3
Dimension Size (in)
MinMax
Head Diameter 2.791 2.938
Head Height 0.827 Not specified
Hex Socket Size 1 ( in)
Inch to Metric Converter
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Frequently Asked Questions

What is the tap drill size for 1-1/2″-6, 1-1/2″-12, and 1-1/2″-18 screws or bolt?

The appropriate tap drill depends on the material and required thread engagement. For aluminum, brass, or plastic (75% thread), a 1-11/32″ (1.344″) drill bit is specified for 1-1/2″-6, a 1-27/64″ (1.422″) for 1-1/2″-12, and a 1-7/16″ (1.438″) for 1-1/2″-18. For steel, stainless, or iron (50% thread), a 1-25/64″ (1.391″) drill bit is recommended for 1-1/2″-6, a 1-7/16″ (1.438″) for 1-1/2″-12, and a 1-29/64″ (1.453″) for 1-1/2″-18.

What clearance hole size is needed for a 1-1/2″ bolt or screw?

For a Close Fit, a 1-33/64″ (1.516″) drill bit is utilized. For a Normal/Free Fit (standard clearance), a 1-17/32″ (1.531″) drill bit is specified.

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.