#3 screw dimensions and bolt sizes are commonly used for precision instrumentation, specialized electronics, and legacy mechanical assemblies. This size features a 0.099″ nominal major diameter and is available in #3-48 coarse (UNC) or #3-56 fine (UNF), representing 48 and 56 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.
#3-48 UNC Screw & Bolt – ANSI/ASME B1.1
Dimension
Size (in)
Min
Max
Major Diameter
0.0938
0.0983
Pitch Diameter
0.0825
0.0848
Minor Diameter
Not specified
0.0735
Threads Per Inch (TPI)
48
Major Diameter
0.0945
0.099
Pitch Diameter
0.0838
0.0855
Minor Diameter
Not specified
0.0742
Threads Per Inch (TPI)
48
#3-56 UNF Screw & Bolt – ANSI/ASME B1.1
Dimension
Size (in)
Min
Max
Major Diameter
0.0942
0.0983
Pitch Diameter
0.0845
0.0867
Minor Diameter
Not specified
0.077
Threads Per Inch (TPI)
56
Major Diameter
0.0949
0.099
Pitch Diameter
0.0858
0.0874
Minor Diameter
Not specified
0.0777
Threads Per Inch (TPI)
56
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 tap drill size for #3-48 and #3-56 screws or bolts?
For aluminum, brass, or plastic (75% thread), a #47 (0.079″) drill bit is commonly used for #3-48, and a #45 (0.082″) for #3-56. For steel, stainless, or iron (50% thread), a #44 (0.086″) drill bit is specified for #3-48 and a #43 (0.089″) for #3-56.
What clearance hole size is needed for a #3 screw or bolt?
A #37 (0.104″) drill bit is specified for a Close Fit, while a #35 (0.110″) drill bit is recommended for a Free Fit.
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.
