#6-40 UNF Thread Specs
Standard: ASME B1.1 (UNF)
Find the technical dimensions, threads per inch (TPI), and tapping guidelines for the #6-40 UNF unified thread.
Compliant with the ASME B1.1 standard, this size has a nominal major diameter of 0.138 inches (3.51 mm) with a pitch of 0.025 inches (TPI of 40).
For general engineering or fastening, the standard recommended tap drill is 0.113 inches (2.87 mm) to achieve adequate thread engagement.
Dimensional Specifications (Inches & mm)
Size Designation
#6-40 UNF
Major Diameter (Nominal)
0.138 in(3.51 mm)
TPI (Threads per Inch)
40
Pitch
0.025 in
Pitch Diameter
0.1218 in(3.09 mm)
Minor Diameter (Ext)
0.1109 in(2.82 mm)
Minor Diameter (Int)
0.1136 in(2.89 mm)
Thread Height
0.0217 in
Drilling & Strength Specs
Tap Drill Size
0.113 in(2.87 mm)
Stress Area
0.0101 in²(6.54 mm²)
Quick Unit Converter
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Frequently Asked Questions
What is the tap drill size for #6-40 UNF?
The recommended tap drill size for a #6-40 UNF thread is 0.113 inches (approx. 2.87 mm) to achieve standard thread engagement.
How many threads per inch (TPI) does a #6-40 UNF bolt have?
A standard #6-40 UNF thread has exactly 40 threads per inch (TPI), with a corresponding linear pitch of 0.025 inches.
What is the major diameter of a #6-40 UNF thread in millimeters?
The nominal major diameter of a #6-40 UNF thread is 0.138 inches, which converts to 3.51 mm.