#1 bolt or screw dimensions and sizes are commonly used for small-scale electronics, precision instrumentation, and model-making assemblies. This size have a 0.074″ nominal major diameter and is available in #1-64 coarse (UNC) or #1-72 fine (UNF), representing 64 and 72 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.
#1-64 UNC Screw & Bolt – ANSI/ASME B1.1
Dimension
Size (in)
Min
Max
Major Diameter
0.0686
0.0724
Pitch Diameter
0.0603
0.0623
Minor Diameter
Not specified
0.0538
Threads Per Inch (TPI)
64
Major Diameter
0.0692
0.073
Pitch Diameter
0.0614
0.0629
Minor Diameter
Not specified
0.0544
Threads Per Inch (TPI)
64
#1-72 UNF Screw & Bolt – ANSI/ASME B1.1
Dimension
Size (in)
Min
Max
Major Diameter
0.0689
0.0724
Pitch Diameter
0.0615
0.0634
Minor Diameter
Not specified
0.0559
Threads Per Inch (TPI)
72
Major Diameter
0.0695
0.073
Pitch Diameter
0.0626
0.064
Minor Diameter
Not specified
0.0565
Threads Per Inch (TPI)
72
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.
For aluminum, brass, or plastic (75% thread), a #53 (0.060″) drill bit is specified for both #1-64 and #1-72 threads. For steel, stainless, or iron (50% thread), a 1/16″ (0.063″) drill bit is used for #1-64, while a #52 (0.064″) drill bit is used for #1-72.
What clearance hole size is needed for a #1?
A #48 (0.076″) drill bit is recommended for a Close Fit. For a Free Fit, a #46 (0.081″) 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.
