#6 screw dimensions and bolt sizes are widely used for PC hardware, electrical wall plates, household fixtures, and general-purpose mechanical fastening. This size have a 0.138″ nominal major diameter and is available in #6-32 coarse (UNC) or #6-40 fine (UNF), representing 32 and 40 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.
#6-32 UNC Screw & Bolt – ANSI/ASME B1.1
Dimension
Size (in)
Min
Max
Major Diameter
0.1312
0.1372
Pitch Diameter
0.1141
0.1169
Minor Diameter
Not specified
0.1
Threads Per Inch (TPI)
32
Major Diameter
0.132
0.138
Pitch Diameter
0.1156
0.1177
Minor Diameter
Not specified
0.1008
Threads Per Inch (TPI)
32
#6-40 UNF Screw & Bolt – ANSI/ASME B1.1
Dimension
Size (in)
Min
Max
Major Diameter
0.1321
0.1372
Pitch Diameter
0.1184
0.121
Minor Diameter
Not specified
0.1074
Threads Per Inch (TPI)
40
Major Diameter
0.1329
0.138
Pitch Diameter
0.1198
0.1218
Minor Diameter
Not specified
0.1082
Threads Per Inch (TPI)
40
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 #6-32 and #6-40 screws or bolts?
For aluminum, brass, or plastic (75% thread), a #36 (0.107″) drill bit is recommended for #6-32 and a #33 (0.113″) for #6-40. For steel, stainless, or iron (50% thread), a #32 (0.116″) drill bit is used for #6-32 and a #31 (0.120″) for #6-40.
What clearance hole size is needed for a #6 bolt or screw?
A #27 (0.144″) drill bit is specified for a Close Fit. For a Free Fit, a #25 (0.150″) drill bit is utilized.
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.
