1-3/8-6 UNC Thread Specs
Standard: ASME B1.1 (UNC)
Find the technical dimensions, threads per inch (TPI), and tapping guidelines for the 1-3/8-6 UNC unified thread.
Compliant with the ASME B1.1 standard, this size has a nominal major diameter of 1.375 inches (34.92 mm) with a pitch of 0.16667 inches (TPI of 6).
For general engineering or fastening, the standard recommended tap drill is 1.2083 inches (30.69 mm) to achieve adequate thread engagement.
Dimensional Specifications (Inches & mm)
Size Designation
1-3/8-6 UNC
Major Diameter (Nominal)
1.375 in(34.92 mm)
TPI (Threads per Inch)
6
Pitch
0.16667 in
Pitch Diameter
1.2667 in(32.18 mm)
Minor Diameter (Ext)
1.1946 in(30.34 mm)
Minor Diameter (Int)
1.2126 in(30.8 mm)
Thread Height
0.1443 in
Drilling & Strength Specs
Tap Drill Size
1.2083 in(30.69 mm)
Stress Area
1.1549 in²(745.08 mm²)
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Frequently Asked Questions
What is the tap drill size for 1-3/8-6 UNC?
The recommended tap drill size for a 1-3/8-6 UNC thread is 1.2083 inches (approx. 30.69 mm) to achieve standard thread engagement.
How many threads per inch (TPI) does a 1-3/8-6 UNC bolt have?
A standard 1-3/8-6 UNC thread has exactly 6 threads per inch (TPI), with a corresponding linear pitch of 0.16667 inches.
What is the major diameter of a 1-3/8-6 UNC thread in millimeters?
The nominal major diameter of a 1-3/8-6 UNC thread is 1.375 inches, which converts to 34.92 mm.