1-3/8-12 UNF Thread Specs
Standard: ASME B1.1 (UNF)
Find the technical dimensions, threads per inch (TPI), and tapping guidelines for the 1-3/8-12 UNF 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 0.08333 inches (TPI of 12).
For general engineering or fastening, the standard recommended tap drill is 1.2917 inches (32.81 mm) to achieve adequate thread engagement.
Dimensional Specifications (Inches & mm)
Size Designation
1-3/8-12 UNF
Major Diameter (Nominal)
1.375 in(34.92 mm)
TPI (Threads per Inch)
12
Pitch
0.08333 in
Pitch Diameter
1.3209 in(33.55 mm)
Minor Diameter (Ext)
1.2848 in(32.63 mm)
Minor Diameter (Int)
1.2938 in(32.86 mm)
Thread Height
0.0722 in
Drilling & Strength Specs
Tap Drill Size
1.2917 in(32.81 mm)
Stress Area
1.3147 in²(848.2 mm²)
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Frequently Asked Questions
What is the tap drill size for 1-3/8-12 UNF?
The recommended tap drill size for a 1-3/8-12 UNF thread is 1.2917 inches (approx. 32.81 mm) to achieve standard thread engagement.
How many threads per inch (TPI) does a 1-3/8-12 UNF bolt have?
A standard 1-3/8-12 UNF thread has exactly 12 threads per inch (TPI), with a corresponding linear pitch of 0.08333 inches.
What is the major diameter of a 1-3/8-12 UNF thread in millimeters?
The nominal major diameter of a 1-3/8-12 UNF thread is 1.375 inches, which converts to 34.92 mm.