1-1/8” Bolt & Screw Dimensions: Diameter & Head Size

1-1/8″ bolt dimensions and bolt sizes are specified for heavy industrial infrastructure, large engine mounts, and critical structural assemblies. This size have a 1.125″ nominal major diameter and is available in 1-1/8″-7 coarse (UNC), 1-1/8″-12 fine (UNF), or 1-1/8″-18 extra-fine (UNEF) thread pitches, representing 7, 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
1-1/8-7 UNC Screw & Bolt – ANSI/ASME B1.1
Dimension Size (in)
Min Max
Major Diameter 1.0982 1.1228
Pitch Diameter 1.0191 1.03
Minor Diameter Not specified 0.9527
Threads Per Inch (TPI) 7
Major Diameter 1.1064 1.1228
Pitch Diameter 1.0228 1.03
Minor Diameter Not specified 0.9527
Threads Per Inch (TPI) 7
Major Diameter 1.1086 1.125
Pitch Diameter 1.0268 1.0322
Minor Diameter Not specified 0.9549
Threads Per Inch (TPI) 7
1-1/8-8 UN Screw & Bolt – ANSI/ASME B1.1
Dimension Size (in)
Min Max
Major Diameter 1.1079 1.1229
Pitch Diameter 1.0348 1.0417
Minor Diameter Not specified 0.9741
Threads Per Inch (TPI) 8
Major Diameter 1.11 1.125
Pitch Diameter 1.0386 1.0438
Minor Diameter Not specified 0.9762
Threads Per Inch (TPI) 8
1-1/8-12 UNF Screw & Bolt – ANSI/ASME B1.1
Dimension Size (in)
Min Max
Major Diameter 1.106 1.1232
Pitch Diameter 1.0601 1.0691
Minor Diameter Not specified 1.024
Threads Per Inch (TPI) 12
Major Diameter 1.1118 1.1232
Pitch Diameter 1.0631 1.0691
Minor Diameter Not specified 1.024
Threads Per Inch (TPI) 12
Major Diameter 1.1136 1.125
Pitch Diameter 1.0664 1.0709
Minor Diameter Not specified 1.0258
Threads Per Inch (TPI) 12
1-1/8-16 UN Screw & Bolt – ANSI/ASME B1.1
Dimension Size (in)
Min Max
Major Diameter 1.1141 1.1235
Pitch Diameter 1.0779 1.0829
Minor Diameter Not specified 1.0491
Threads Per Inch (TPI) 16
Major Diameter 1.1156 1.125
Pitch Diameter 1.0806 1.0844
Minor Diameter Not specified 1.0506
Threads Per Inch (TPI) 16
1-1/8-18 UNEF Screw & Bolt – ANSI/ASME B1.1
Dimension Size (in)
Min Max
Major Diameter 1.1149 1.1236
Pitch Diameter 1.0827 1.0875
Minor Diameter Not specified 1.0574
Threads Per Inch (TPI) 18
Major Diameter 1.1163 1.125
Pitch Diameter 1.0853 1.0889
Minor Diameter Not specified 1.0588
Threads Per Inch (TPI) 18
1-1/8-20 UN Screw & Bolt – ANSI/ASME B1.1
Dimension Size (in)
Min Max
Major Diameter 1.1155 1.1236
Pitch Diameter 1.0865 1.0911
Minor Diameter Not specified 1.0641
Threads Per Inch (TPI) 20
Major Diameter 1.1169 1.125
Pitch Diameter 1.089 1.0925
Minor Diameter Not specified 1.0655
Threads Per Inch (TPI) 20
1-1/8-28 UN Screw & Bolt – ANSI/ASME B1.1
Dimension Size (in)
Min Max
Major Diameter 1.1173 1.1238
Pitch Diameter 1.0966 1.1006
Minor Diameter Not specified 1.0813
Threads Per Inch (TPI) 28
Major Diameter 1.1185 1.125
Pitch Diameter 1.0988 1.1018
Minor Diameter Not specified 1.0825
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 1.631 1.688
Width Across Corners 1.859 1.949
Head Height 0.658 0.78
Hex Socket Cap Head – ANSI/ASME B18.3
Dimension Size (in)
MinMax
Head Diameter 1.665 1.688
Head Height 1.111 1.125
Hex Socket Size 7/8 (0.875 in)
Hex Socket Flat Head – ANSI/ASME B18.3
Dimension Size (in)
MinMax
Head Diameter 2.079 2.188
Head Height 0.611 Not specified
Hex Socket Size 3/4 (0.75 in)
Inch to Metric Converter
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Frequently Asked Questions

What is the tap drill size for 1-1/8″-7, 1-1/8″-12, and 1-1/8″-18 screws or bolts?

The appropriate tap drill depends on the material and required thread engagement. For aluminum, brass, or plastic (75% thread), a 63/64″ (0.984″) drill bit is specified for 1-1/8″-7, a 1-3/64″ (1.047″) for 1-1/8″-12, and a 1-1/16″ (1.063″) for 1-1/8″-18. For steel, stainless, or iron (50% thread), a 1-1/32″ (1.031″) drill bit is recommended for 1-1/8″-7, and a 1-5/64″ (1.078″) drill bit is specified for both 1-1/8″-12 and 1-1/8″-18.

What clearance hole size is needed for a 1-1/8″ bolt or screw?

For a Close Fit, a 1-9/64″ (1.141″) drill bit is utilized. For a Normal/Free Fit (standard clearance), a 1-5/32″ (1.156″) drill bit is specified to allow the screw or bolt body to pass through the material without binding.

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.